number of literature review in thesis

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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

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Methodology

• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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See an example

Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

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To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

Scribbr slides are free to use, customize, and distribute for educational purposes.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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McCombes, S. (2023, September 11). How to Write a Literature Review | Guide, Examples, & Templates. Scribbr. Retrieved August 12, 2024, from https://www.scribbr.com/dissertation/literature-review/

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• What is a Literature Review? | Guide, Template, & Examples

What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

• Quick Run-through
• Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and scholarly context
• Develop a theoretical framework and methodology for your research
• Position yourself in relation to other researchers and theorists
• Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

Prevent plagiarism, run a free check.

Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

• Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
• Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
• Critically evaluate: mention the strengths and weaknesses of your sources.
• Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarise yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your  dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

Cite this Scribbr article

If you want to cite this source, you can copy and paste the citation or click the ‘Cite this Scribbr article’ button to automatically add the citation to our free Reference Generator.

McCombes, S. (2022, June 07). What is a Literature Review? | Guide, Template, & Examples. Scribbr. Retrieved 12 August 2024, from https://www.scribbr.co.uk/thesis-dissertation/literature-review/

Is this article helpful?

Shona McCombes

Other students also liked, how to write a dissertation proposal | a step-by-step guide, what is a theoretical framework | a step-by-step guide, what is a research methodology | steps & tips.

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What is a literature review?

​Scholarship can be seen as an ongoing conversation between researchers in a field. When you conduct research and share your findings, you become a participant in these conversations. In order to participate effectively, it is essential that you know what has been discussed, what ideas have gained traction, and what's currently being talked about.

A literature review examines how a particular topic has been previously approached in a field. It expresses prevailing ideas and understandings, as well as points of debate. Through the literature review, researchers give context to their work and show how their study builds upon previous knowledge and engages with questions of significance.  

As you conduct your literature review, look to collectively analyze the sources you find. Look for commonalities as well as noteworthy differences. Additionally, try to identify existing gaps. What hasn't been studied? What questions remain to be answered?

Suggested Reading

• Literature Reviews: An Overview for Graduate Students
• How to Write a Literature Review
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How to Write a Literature Review

What is a literature review.

• What Is the Literature
• Writing the Review

A literature review is much more than an annotated bibliography or a list of separate reviews of articles and books. It is a critical, analytical summary and synthesis of the current knowledge of a topic. Thus it should compare and relate different theories, findings, etc, rather than just summarize them individually. In addition, it should have a particular focus or theme to organize the review. It does not have to be an exhaustive account of everything published on the topic, but it should discuss all the significant academic literature and other relevant sources important for that focus.

This is meant to be a general guide to writing a literature review: ways to structure one, what to include, how it supplements other research. For more specific help on writing a review, and especially for help on finding the literature to review, sign up for a Personal Research Session .

The specific organization of a literature review depends on the type and purpose of the review, as well as on the specific field or topic being reviewed. But in general, it is a relatively brief but thorough exploration of past and current work on a topic. Rather than a chronological listing of previous work, though, literature reviews are usually organized thematically, such as different theoretical approaches, methodologies, or specific issues or concepts involved in the topic. A thematic organization makes it much easier to examine contrasting perspectives, theoretical approaches, methodologies, findings, etc, and to analyze the strengths and weaknesses of, and point out any gaps in, previous research. And this is the heart of what a literature review is about. A literature review may offer new interpretations, theoretical approaches, or other ideas; if it is part of a research proposal or report it should demonstrate the relationship of the proposed or reported research to others' work; but whatever else it does, it must provide a critical overview of the current state of research efforts. 

Literature reviews are common and very important in the sciences and social sciences. They are less common and have a less important role in the humanities, but they do have a place, especially stand-alone reviews.

Types of Literature Reviews

There are different types of literature reviews, and different purposes for writing a review, but the most common are:

• Stand-alone literature review articles . These provide an overview and analysis of the current state of research on a topic or question. The goal is to evaluate and compare previous research on a topic to provide an analysis of what is currently known, and also to reveal controversies, weaknesses, and gaps in current work, thus pointing to directions for future research. You can find examples published in any number of academic journals, but there is a series of Annual Reviews of *Subject* which are specifically devoted to literature review articles. Writing a stand-alone review is often an effective way to get a good handle on a topic and to develop ideas for your own research program. For example, contrasting theoretical approaches or conflicting interpretations of findings can be the basis of your research project: can you find evidence supporting one interpretation against another, or can you propose an alternative interpretation that overcomes their limitations?
• Part of a research proposal . This could be a proposal for a PhD dissertation, a senior thesis, or a class project. It could also be a submission for a grant. The literature review, by pointing out the current issues and questions concerning a topic, is a crucial part of demonstrating how your proposed research will contribute to the field, and thus of convincing your thesis committee to allow you to pursue the topic of your interest or a funding agency to pay for your research efforts.
• Part of a research report . When you finish your research and write your thesis or paper to present your findings, it should include a literature review to provide the context to which your work is a contribution. Your report, in addition to detailing the methods, results, etc. of your research, should show how your work relates to others' work.

A literature review for a research report is often a revision of the review for a research proposal, which can be a revision of a stand-alone review. Each revision should be a fairly extensive revision. With the increased knowledge of and experience in the topic as you proceed, your understanding of the topic will increase. Thus, you will be in a better position to analyze and critique the literature. In addition, your focus will change as you proceed in your research. Some areas of the literature you initially reviewed will be marginal or irrelevant for your eventual research, and you will need to explore other areas more thoroughly. 

Examples of Literature Reviews

See the series of Annual Reviews of *Subject* which are specifically devoted to literature review articles to find many examples of stand-alone literature reviews in the biomedical, physical, and social sciences. 

Research report articles vary in how they are organized, but a common general structure is to have sections such as:

• Abstract - Brief summary of the contents of the article
• Introduction - A explanation of the purpose of the study, a statement of the research question(s) the study intends to address
• Literature review - A critical assessment of the work done so far on this topic, to show how the current study relates to what has already been done
• Methods - How the study was carried out (e.g. instruments or equipment, procedures, methods to gather and analyze data)
• Results - What was found in the course of the study
• Discussion - What do the results mean
• Conclusion - State the conclusions and implications of the results, and discuss how it relates to the work reviewed in the literature review; also, point to directions for further work in the area

Here are some articles that illustrate variations on this theme. There is no need to read the entire articles (unless the contents interest you); just quickly browse through to see the sections, and see how each section is introduced and what is contained in them.

The Determinants of Undergraduate Grade Point Average: The Relative Importance of Family Background, High School Resources, and Peer Group Effects , in The Journal of Human Resources , v. 34 no. 2 (Spring 1999), p. 268-293.

This article has a standard breakdown of sections:

• Introduction
• Literature Review
• Some discussion sections

First Encounters of the Bureaucratic Kind: Early Freshman Experiences with a Campus Bureaucracy , in The Journal of Higher Education , v. 67 no. 6 (Nov-Dec 1996), p. 660-691.

This one does not have a section specifically labeled as a "literature review" or "review of the literature," but the first few sections cite a long list of other sources discussing previous research in the area before the authors present their own study they are reporting.

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• Last Updated: Jan 11, 2024 9:48 AM
• URL: https://libguides.wesleyan.edu/litreview

How to Conduct a Literature Review: A Guide for Graduate Students

• Let's Get Started!
• Traditional or Narrative Reviews
• Systematic Reviews
• Typology of Reviews
• Literature Review Resources
• Developing a Search Strategy
• What Literature to Search
• Where to Search: Indexes and Databases
• Finding articles: Libkey Nomad
• Finding Dissertations and Theses
• Extending Your Searching with Citation Chains
• Forward Citation Chains - Cited Reference Searching
• Keeping up with the Literature
• Managing Your References
• Need More Information?

Bookmark This Guide!

https://instr.iastate.libguides.com/gradlitrev

Where to Get Help

Librarians at ISU are subject experts who can help with your research and course needs. There are experts available for every discipline at ISU who are ready to assist you with your information needs!

What we do:

• Answer questions via phone, chat and in-person
• Consult with student and faculty researchers on request
• Purchase materials for the collection
• Teach instruction session for ISU courses
• Support faculty getting ready for promotion & tenure reviews
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Find Your Librarian

   “Google can bring you back 100,000 answers. A librarian can bring you back the right one.” - Neil Gaiman

The literature review is an important part of your thesis or dissertation. It is a survey of existing literature that provides context for your research contribution, and demonstrates your subject knowledge. It is also the way to tell the story of how your research extends knowledge in your field.

The first step to writing a successful literature review is knowing how to find and evaluate literature in your field. This guide is designed to introduce you to tools and give you skills you can use to effectively find the resources needed for your literature review.

Before getting started, familiarize yourself with some essential resources provided by the Graduate College:

• Dissertation and Thesis Information
• Center for Communication Excellence
• Graduate College Handbook

Below are some questions that you can discuss with your advisor as you begin your research:

Questions to ask as you think about your literature review:

What is my research question.

Choosing a valid research question is something you will need to discuss with your academic advisor and/or POS committee. Ideas for your topic may come from your coursework, lab rotations, or work as a research assistant. Having a specific research topic allows you to focus your research on a project that is manageable. Beginning work on your literature review can help narrow your topic.

What kind of literature review is appropriate for my research question?

Depending on your area of research, the type of literature review you do for your thesis will vary. Consult with your advisor about the requirements for your discipline. You can view theses and dissertations from your field in the library's Digital Repository can give you ideas about how your literature review should be structured.

What kind of literature should I use?

The kind of literature you use for your thesis will depend on your discipline. The Library has developed a list of Guides by Subject with discipline-specific resources. For a given subject area, look for the guide titles "[Discipline] Research Guide." You may also consult our liaison librarians for information about the literature available your research area.

How will I make sure that I find all the appropriate information that informs my research?

Consulting multiple sources of information is the best way to insure that you have done a comprehensive search of the literature in your area. The What Literature to Search tab has information about the types of resources you may need to search. You may also consult our liaison librarians for assistance with identifying resources..

How will I evaluate the literature to include trustworthy information and eliminate unnecessary or untrustworthy information?

While you are searching for relevant information about your topic you will need to think about the accuracy of the information, whether the information is from a reputable source, whether it is objective and current. Our guides about Evaluating Scholarly Books and Articles and Evaluating Websites will give you criteria to use when evaluating resources.

How should I organize my literature? What citation management program is best for me?

Citation management software can help you organize your references in folders and/or with tags. You can also annotate and highlight the PDFs within the software and usually the notes are searchable. To choose a good citation management software, you need to consider which one can be streamlined with your literature search and writing process. Here is a guide page comparing EndNote, Mendeley & Zotero. The Library also has guides for three of the major citation management tools:

• EndNote & EndNote Web Guide
• Mendeley Guide
• Getting Started with Zotero

What steps should I take to ensure academic integrity?

The best way to ensure academic integrity is to familiarize yourself with different types of intentional and unintentional plagiarism and learn about the University's standards for academic integrity. Start with this guide . The Library also has a guide about your rights and responsibilities regarding copyrighted images and figures that you include in your thesis.

Where can I find writing and editing help?

Writing and editing help is available at the Graduate College's Center for Communication Excellence . The CCE offers individual consultations, peer writing groups, workshops and seminars to help you improve your writing.

Where can I find I find formatting standards? Technical support?

The Graduate College has a Dissertation/ Thesis website with extensive examples and videos about formatting theses and dissertations. The site also has templates and formatting instructions for Word and LaTex .

What citation style should I use?

The Graduate College thesis guidelines require that you "use a consistent, current academic style for your discipline." The Library has a Citation Style Guides resource you can use for guidance on specific citation styles. If you are not sure, please consult your advisor or liaison librarians for help.

Adapted from The Literature Review: For Dissertations, by the University of Michigan Library. Available: https://guides.lib.umich.edu/dissertationlitreview

Center for Communication Excellence/ Library Workshop Slides

Slides from the CCE/ Library Workshop "A Citation Here...A Citation There...Pretty Soon You'll Have a Lit Review" held on February 21, 2024 are below:

• CCE Workshop February 21, 2024
• Next: Types of Literature Reviews >>

The library's collections and services are available to all ISU students, faculty, and staff and Parks Library is open to the public .

• Last Updated: Aug 12, 2024 4:07 PM
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What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

• What is the purpose of literature review? 
• a. Habitat Loss and Species Extinction: 
• b. Range Shifts and Phenological Changes: 
• c. Ocean Acidification and Coral Reefs: 
• d. Adaptive Strategies and Conservation Efforts: 

How to write a good literature review 

• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• How to write a literature review faster with Paperpal? 
• Frequently asked questions 

What is a literature review?

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

What is the purpose of literature review?

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

1. Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 

2. Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field. 

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3. Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 

4. Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 

5. Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 

6. Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

a. Habitat Loss and Species Extinction:

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

b. Range Shifts and Phenological Changes:

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

c. Ocean Acidification and Coral Reefs:

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

d. Adaptive Strategies and Conservation Efforts:

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

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Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

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Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

Whether you’re exploring a new research field or finding new angles to develop an existing topic, sifting through hundreds of papers can take more time than you have to spare. But what if you could find science-backed insights with verified citations in seconds? That’s the power of Paperpal’s new Research feature!  

How to write a literature review faster with Paperpal?

Paperpal, an AI writing assistant, integrates powerful academic search capabilities within its writing platform. With the Research feature, you get 100% factual insights, with citations backed by 250M+ verified research articles, directly within your writing interface with the option to save relevant references in your Citation Library. By eliminating the need to switch tabs to find answers to all your research questions, Paperpal saves time and helps you stay focused on your writing.   

Here’s how to use the Research feature:  

• Ask a question: Get started with a new document on paperpal.com. Click on the “Research” feature and type your question in plain English. Paperpal will scour over 250 million research articles, including conference papers and preprints, to provide you with accurate insights and citations. 
• Review and Save: Paperpal summarizes the information, while citing sources and listing relevant reads. You can quickly scan the results to identify relevant references and save these directly to your built-in citations library for later access. 
• Cite with Confidence: Paperpal makes it easy to incorporate relevant citations and references into your writing, ensuring your arguments are well-supported by credible sources. This translates to a polished, well-researched literature review. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a good literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. By combining effortless research with an easy citation process, Paperpal Research streamlines the literature review process and empowers you to write faster and with more confidence. Try Paperpal Research now and see for yourself.  

Frequently asked questions

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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How To Structure Your Literature Review

3 options to help structure your chapter.

By: Amy Rommelspacher (PhD) | Reviewer: Dr Eunice Rautenbach | November 2020 (Updated May 2023)

Writing the literature review chapter can seem pretty daunting when you’re piecing together your dissertation or thesis. As  we’ve discussed before , a good literature review needs to achieve a few very important objectives – it should:

• Demonstrate your knowledge of the research topic
• Identify the gaps in the literature and show how your research links to these
• Provide the foundation for your conceptual framework (if you have one)
• Inform your own  methodology and research design

To achieve this, your literature review needs a well-thought-out structure . Get the structure of your literature review chapter wrong and you’ll struggle to achieve these objectives. Don’t worry though – in this post, we’ll look at how to structure your literature review for maximum impact (and marks!).

But wait – is this the right time?

Deciding on the structure of your literature review should come towards the end of the literature review process – after you have collected and digested the literature, but before you start writing the chapter. 

In other words, you need to first develop a rich understanding of the literature before you even attempt to map out a structure. There’s no use trying to develop a structure before you’ve fully wrapped your head around the existing research.

Equally importantly, you need to have a structure in place before you start writing , or your literature review will most likely end up a rambling, disjointed mess. 

Importantly, don’t feel that once you’ve defined a structure you can’t iterate on it. It’s perfectly natural to adjust as you engage in the writing process. As we’ve discussed before , writing is a way of developing your thinking, so it’s quite common for your thinking to change – and therefore, for your chapter structure to change – as you write. 

Need a helping hand?

Like any other chapter in your thesis or dissertation, your literature review needs to have a clear, logical structure. At a minimum, it should have three essential components – an  introduction , a  body   and a  conclusion . 

Let’s take a closer look at each of these.

1: The Introduction Section

Just like any good introduction, the introduction section of your literature review should introduce the purpose and layout (organisation) of the chapter. In other words, your introduction needs to give the reader a taste of what’s to come, and how you’re going to lay that out. Essentially, you should provide the reader with a high-level roadmap of your chapter to give them a taste of the journey that lies ahead.

Here’s an example of the layout visualised in a literature review introduction:

Your introduction should also outline your topic (including any tricky terminology or jargon) and provide an explanation of the scope of your literature review – in other words, what you  will   and  won’t   be covering (the delimitations ). This helps ringfence your review and achieve a clear focus . The clearer and narrower your focus, the deeper you can dive into the topic (which is typically where the magic lies). 

Depending on the nature of your project, you could also present your stance or point of view at this stage. In other words, after grappling with the literature you’ll have an opinion about what the trends and concerns are in the field as well as what’s lacking. The introduction section can then present these ideas so that it is clear to examiners that you’re aware of how your research connects with existing knowledge .

2: The Body Section

The body of your literature review is the centre of your work. This is where you’ll present, analyse, evaluate and synthesise the existing research. In other words, this is where you’re going to earn (or lose) the most marks. Therefore, it’s important to carefully think about how you will organise your discussion to present it in a clear way. 

The body of your literature review should do just as the description of this chapter suggests. It should “review” the literature – in other words, identify, analyse, and synthesise it. So, when thinking about structuring your literature review, you need to think about which structural approach will provide the best “review” for your specific type of research and objectives (we’ll get to this shortly).

There are (broadly speaking)  three options  for organising your literature review.

Option 1: Chronological (according to date)

Organising the literature chronologically is one of the simplest ways to structure your literature review. You start with what was published first and work your way through the literature until you reach the work published most recently. Pretty straightforward.

The benefit of this option is that it makes it easy to discuss the developments and debates in the field as they emerged over time. Organising your literature chronologically also allows you to highlight how specific articles or pieces of work might have changed the course of the field – in other words, which research has had the most impact . Therefore, this approach is very useful when your research is aimed at understanding how the topic has unfolded over time and is often used by scholars in the field of history. That said, this approach can be utilised by anyone that wants to explore change over time .

For example , if a student of politics is investigating how the understanding of democracy has evolved over time, they could use the chronological approach to provide a narrative that demonstrates how this understanding has changed through the ages.

Here are some questions you can ask yourself to help you structure your literature review chronologically.

• What is the earliest literature published relating to this topic?
• How has the field changed over time? Why?
• What are the most recent discoveries/theories?

In some ways, chronology plays a part whichever way you decide to structure your literature review, because you will always, to a certain extent, be analysing how the literature has developed. However, with the chronological approach, the emphasis is very firmly on how the discussion has evolved over time , as opposed to how all the literature links together (which we’ll discuss next ).

Option 2: Thematic (grouped by theme)

The thematic approach to structuring a literature review means organising your literature by theme or category – for example, by independent variables (i.e. factors that have an impact on a specific outcome).

As you’ve been collecting and synthesising literature , you’ll likely have started seeing some themes or patterns emerging. You can then use these themes or patterns as a structure for your body discussion. The thematic approach is the most common approach and is useful for structuring literature reviews in most fields.

For example, if you were researching which factors contributed towards people trusting an organisation, you might find themes such as consumers’ perceptions of an organisation’s competence, benevolence and integrity. Structuring your literature review thematically would mean structuring your literature review’s body section to discuss each of these themes, one section at a time.

Here are some questions to ask yourself when structuring your literature review by themes:

• Are there any patterns that have come to light in the literature?
• What are the central themes and categories used by the researchers?
• Do I have enough evidence of these themes?

PS – you can see an example of a thematically structured literature review in our literature review sample walkthrough video here.

Option 3: Methodological

The methodological option is a way of structuring your literature review by the research methodologies used . In other words, organising your discussion based on the angle from which each piece of research was approached – for example, qualitative , quantitative or mixed  methodologies.

Structuring your literature review by methodology can be useful if you are drawing research from a variety of disciplines and are critiquing different methodologies. The point of this approach is to question  how  existing research has been conducted, as opposed to  what  the conclusions and/or findings the research were.

For example, a sociologist might centre their research around critiquing specific fieldwork practices. Their literature review will then be a summary of the fieldwork methodologies used by different studies.

Here are some questions you can ask yourself when structuring your literature review according to methodology:

• Which methodologies have been utilised in this field?
• Which methodology is the most popular (and why)?
• What are the strengths and weaknesses of the various methodologies?
• How can the existing methodologies inform my own methodology?

3: The Conclusion Section

Once you’ve completed the body section of your literature review using one of the structural approaches we discussed above, you’ll need to “wrap up” your literature review and pull all the pieces together to set the direction for the rest of your dissertation or thesis.

The conclusion is where you’ll present the key findings of your literature review. In this section, you should emphasise the research that is especially important to your research questions and highlight the gaps that exist in the literature. Based on this, you need to make it clear what you will add to the literature – in other words, justify your own research by showing how it will help fill one or more of the gaps you just identified.

Last but not least, if it’s your intention to develop a conceptual framework for your dissertation or thesis, the conclusion section is a good place to present this.

Example: Thematically Structured Review

In the video below, we unpack a literature review chapter so that you can see an example of a thematically structure review in practice.

Let’s Recap

In this article, we’ve  discussed how to structure your literature review for maximum impact. Here’s a quick recap of what  you need to keep in mind when deciding on your literature review structure:

• Just like other chapters, your literature review needs a clear introduction , body and conclusion .
• The introduction section should provide an overview of what you will discuss in your literature review.
• The body section of your literature review can be organised by chronology , theme or methodology . The right structural approach depends on what you’re trying to achieve with your research.
• The conclusion section should draw together the key findings of your literature review and link them to your research questions.

If you’re ready to get started, be sure to download our free literature review template to fast-track your chapter outline.

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

28 Comments

Great work. This is exactly what I was looking for and helps a lot together with your previous post on literature review. One last thing is missing: a link to a great literature chapter of an journal article (maybe with comments of the different sections in this review chapter). Do you know any great literature review chapters?

I agree with you Marin… A great piece

I agree with Marin. This would be quite helpful if you annotate a nicely structured literature from previously published research articles.

Awesome article for my research.

I thank you immensely for this wonderful guide

It is indeed thought and supportive work for the futurist researcher and students

Very educative and good time to get guide. Thank you

Great work, very insightful. Thank you.

Thanks for this wonderful presentation. My question is that do I put all the variables into a single conceptual framework or each hypothesis will have it own conceptual framework?

Thank you very much, very helpful

This is very educative and precise . Thank you very much for dropping this kind of write up .

Pheeww, so damn helpful, thank you for this informative piece.

I’m doing a research project topic ; stool analysis for parasitic worm (enteric) worm, how do I structure it, thanks.

comprehensive explanation. Help us by pasting the URL of some good “literature review” for better understanding.

great piece. thanks for the awesome explanation. it is really worth sharing. I have a little question, if anyone can help me out, which of the options in the body of literature can be best fit if you are writing an architectural thesis that deals with design?

I am doing a research on nanofluids how can l structure it?

Beautifully clear.nThank you!

Lucid! Thankyou!

Brilliant work, well understood, many thanks

I like how this was so clear with simple language 😊😊 thank you so much 😊 for these information 😊

Insightful. I was struggling to come up with a sensible literature review but this has been really helpful. Thank you!

You have given thought-provoking information about the review of the literature.

Thank you. It has made my own research better and to impart your work to students I teach

I learnt a lot from this teaching. It’s a great piece.

I am doing research on EFL teacher motivation for his/her job. How Can I structure it? Is there any detailed template, additional to this?

You are so cool! I do not think I’ve read through something like this before. So nice to find somebody with some genuine thoughts on this issue. Seriously.. thank you for starting this up. This site is one thing that is required on the internet, someone with a little originality!

I’m asked to do conceptual, theoretical and empirical literature, and i just don’t know how to structure it

Asking questions are actually fastidious thing if you are not understanding anything fully, but this article presents good understanding yet.

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Ten Simple Rules for Writing a Literature Review

Marco pautasso.

1 Centre for Functional and Evolutionary Ecology (CEFE), CNRS, Montpellier, France

2 Centre for Biodiversity Synthesis and Analysis (CESAB), FRB, Aix-en-Provence, France

Literature reviews are in great demand in most scientific fields. Their need stems from the ever-increasing output of scientific publications [1] . For example, compared to 1991, in 2008 three, eight, and forty times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively [2] . Given such mountains of papers, scientists cannot be expected to examine in detail every single new paper relevant to their interests [3] . Thus, it is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews can lead to new synthetic insights and are often widely read [4] . For such summaries to be useful, however, they need to be compiled in a professional way [5] .

When starting from scratch, reviewing the literature can require a titanic amount of work. That is why researchers who have spent their career working on a certain research issue are in a perfect position to review that literature. Some graduate schools are now offering courses in reviewing the literature, given that most research students start their project by producing an overview of what has already been done on their research issue [6] . However, it is likely that most scientists have not thought in detail about how to approach and carry out a literature review.

Reviewing the literature requires the ability to juggle multiple tasks, from finding and evaluating relevant material to synthesising information from various sources, from critical thinking to paraphrasing, evaluating, and citation skills [7] . In this contribution, I share ten simple rules I learned working on about 25 literature reviews as a PhD and postdoctoral student. Ideas and insights also come from discussions with coauthors and colleagues, as well as feedback from reviewers and editors.

Rule 1: Define a Topic and Audience

How to choose which topic to review? There are so many issues in contemporary science that you could spend a lifetime of attending conferences and reading the literature just pondering what to review. On the one hand, if you take several years to choose, several other people may have had the same idea in the meantime. On the other hand, only a well-considered topic is likely to lead to a brilliant literature review [8] . The topic must at least be:

• interesting to you (ideally, you should have come across a series of recent papers related to your line of work that call for a critical summary),
• an important aspect of the field (so that many readers will be interested in the review and there will be enough material to write it), and
• a well-defined issue (otherwise you could potentially include thousands of publications, which would make the review unhelpful).

Ideas for potential reviews may come from papers providing lists of key research questions to be answered [9] , but also from serendipitous moments during desultory reading and discussions. In addition to choosing your topic, you should also select a target audience. In many cases, the topic (e.g., web services in computational biology) will automatically define an audience (e.g., computational biologists), but that same topic may also be of interest to neighbouring fields (e.g., computer science, biology, etc.).

Rule 2: Search and Re-search the Literature

After having chosen your topic and audience, start by checking the literature and downloading relevant papers. Five pieces of advice here:

• keep track of the search items you use (so that your search can be replicated [10] ),
• keep a list of papers whose pdfs you cannot access immediately (so as to retrieve them later with alternative strategies),
• use a paper management system (e.g., Mendeley, Papers, Qiqqa, Sente),
• define early in the process some criteria for exclusion of irrelevant papers (these criteria can then be described in the review to help define its scope), and
• do not just look for research papers in the area you wish to review, but also seek previous reviews.

The chances are high that someone will already have published a literature review ( Figure 1 ), if not exactly on the issue you are planning to tackle, at least on a related topic. If there are already a few or several reviews of the literature on your issue, my advice is not to give up, but to carry on with your own literature review,

The bottom-right situation (many literature reviews but few research papers) is not just a theoretical situation; it applies, for example, to the study of the impacts of climate change on plant diseases, where there appear to be more literature reviews than research studies [33] .

• discussing in your review the approaches, limitations, and conclusions of past reviews,
• trying to find a new angle that has not been covered adequately in the previous reviews, and
• incorporating new material that has inevitably accumulated since their appearance.

When searching the literature for pertinent papers and reviews, the usual rules apply:

• be thorough,
• use different keywords and database sources (e.g., DBLP, Google Scholar, ISI Proceedings, JSTOR Search, Medline, Scopus, Web of Science), and
• look at who has cited past relevant papers and book chapters.

Rule 3: Take Notes While Reading

If you read the papers first, and only afterwards start writing the review, you will need a very good memory to remember who wrote what, and what your impressions and associations were while reading each single paper. My advice is, while reading, to start writing down interesting pieces of information, insights about how to organize the review, and thoughts on what to write. This way, by the time you have read the literature you selected, you will already have a rough draft of the review.

Of course, this draft will still need much rewriting, restructuring, and rethinking to obtain a text with a coherent argument [11] , but you will have avoided the danger posed by staring at a blank document. Be careful when taking notes to use quotation marks if you are provisionally copying verbatim from the literature. It is advisable then to reformulate such quotes with your own words in the final draft. It is important to be careful in noting the references already at this stage, so as to avoid misattributions. Using referencing software from the very beginning of your endeavour will save you time.

Rule 4: Choose the Type of Review You Wish to Write

After having taken notes while reading the literature, you will have a rough idea of the amount of material available for the review. This is probably a good time to decide whether to go for a mini- or a full review. Some journals are now favouring the publication of rather short reviews focusing on the last few years, with a limit on the number of words and citations. A mini-review is not necessarily a minor review: it may well attract more attention from busy readers, although it will inevitably simplify some issues and leave out some relevant material due to space limitations. A full review will have the advantage of more freedom to cover in detail the complexities of a particular scientific development, but may then be left in the pile of the very important papers “to be read” by readers with little time to spare for major monographs.

There is probably a continuum between mini- and full reviews. The same point applies to the dichotomy of descriptive vs. integrative reviews. While descriptive reviews focus on the methodology, findings, and interpretation of each reviewed study, integrative reviews attempt to find common ideas and concepts from the reviewed material [12] . A similar distinction exists between narrative and systematic reviews: while narrative reviews are qualitative, systematic reviews attempt to test a hypothesis based on the published evidence, which is gathered using a predefined protocol to reduce bias [13] , [14] . When systematic reviews analyse quantitative results in a quantitative way, they become meta-analyses. The choice between different review types will have to be made on a case-by-case basis, depending not just on the nature of the material found and the preferences of the target journal(s), but also on the time available to write the review and the number of coauthors [15] .

Rule 5: Keep the Review Focused, but Make It of Broad Interest

Whether your plan is to write a mini- or a full review, it is good advice to keep it focused 16 , 17 . Including material just for the sake of it can easily lead to reviews that are trying to do too many things at once. The need to keep a review focused can be problematic for interdisciplinary reviews, where the aim is to bridge the gap between fields [18] . If you are writing a review on, for example, how epidemiological approaches are used in modelling the spread of ideas, you may be inclined to include material from both parent fields, epidemiology and the study of cultural diffusion. This may be necessary to some extent, but in this case a focused review would only deal in detail with those studies at the interface between epidemiology and the spread of ideas.

While focus is an important feature of a successful review, this requirement has to be balanced with the need to make the review relevant to a broad audience. This square may be circled by discussing the wider implications of the reviewed topic for other disciplines.

Rule 6: Be Critical and Consistent

Reviewing the literature is not stamp collecting. A good review does not just summarize the literature, but discusses it critically, identifies methodological problems, and points out research gaps [19] . After having read a review of the literature, a reader should have a rough idea of:

• the major achievements in the reviewed field,
• the main areas of debate, and
• the outstanding research questions.

It is challenging to achieve a successful review on all these fronts. A solution can be to involve a set of complementary coauthors: some people are excellent at mapping what has been achieved, some others are very good at identifying dark clouds on the horizon, and some have instead a knack at predicting where solutions are going to come from. If your journal club has exactly this sort of team, then you should definitely write a review of the literature! In addition to critical thinking, a literature review needs consistency, for example in the choice of passive vs. active voice and present vs. past tense.

Rule 7: Find a Logical Structure

Like a well-baked cake, a good review has a number of telling features: it is worth the reader's time, timely, systematic, well written, focused, and critical. It also needs a good structure. With reviews, the usual subdivision of research papers into introduction, methods, results, and discussion does not work or is rarely used. However, a general introduction of the context and, toward the end, a recapitulation of the main points covered and take-home messages make sense also in the case of reviews. For systematic reviews, there is a trend towards including information about how the literature was searched (database, keywords, time limits) [20] .

How can you organize the flow of the main body of the review so that the reader will be drawn into and guided through it? It is generally helpful to draw a conceptual scheme of the review, e.g., with mind-mapping techniques. Such diagrams can help recognize a logical way to order and link the various sections of a review [21] . This is the case not just at the writing stage, but also for readers if the diagram is included in the review as a figure. A careful selection of diagrams and figures relevant to the reviewed topic can be very helpful to structure the text too [22] .

Rule 8: Make Use of Feedback

Reviews of the literature are normally peer-reviewed in the same way as research papers, and rightly so [23] . As a rule, incorporating feedback from reviewers greatly helps improve a review draft. Having read the review with a fresh mind, reviewers may spot inaccuracies, inconsistencies, and ambiguities that had not been noticed by the writers due to rereading the typescript too many times. It is however advisable to reread the draft one more time before submission, as a last-minute correction of typos, leaps, and muddled sentences may enable the reviewers to focus on providing advice on the content rather than the form.

Feedback is vital to writing a good review, and should be sought from a variety of colleagues, so as to obtain a diversity of views on the draft. This may lead in some cases to conflicting views on the merits of the paper, and on how to improve it, but such a situation is better than the absence of feedback. A diversity of feedback perspectives on a literature review can help identify where the consensus view stands in the landscape of the current scientific understanding of an issue [24] .

Rule 9: Include Your Own Relevant Research, but Be Objective

In many cases, reviewers of the literature will have published studies relevant to the review they are writing. This could create a conflict of interest: how can reviewers report objectively on their own work [25] ? Some scientists may be overly enthusiastic about what they have published, and thus risk giving too much importance to their own findings in the review. However, bias could also occur in the other direction: some scientists may be unduly dismissive of their own achievements, so that they will tend to downplay their contribution (if any) to a field when reviewing it.

In general, a review of the literature should neither be a public relations brochure nor an exercise in competitive self-denial. If a reviewer is up to the job of producing a well-organized and methodical review, which flows well and provides a service to the readership, then it should be possible to be objective in reviewing one's own relevant findings. In reviews written by multiple authors, this may be achieved by assigning the review of the results of a coauthor to different coauthors.

Rule 10: Be Up-to-Date, but Do Not Forget Older Studies

Given the progressive acceleration in the publication of scientific papers, today's reviews of the literature need awareness not just of the overall direction and achievements of a field of inquiry, but also of the latest studies, so as not to become out-of-date before they have been published. Ideally, a literature review should not identify as a major research gap an issue that has just been addressed in a series of papers in press (the same applies, of course, to older, overlooked studies (“sleeping beauties” [26] )). This implies that literature reviewers would do well to keep an eye on electronic lists of papers in press, given that it can take months before these appear in scientific databases. Some reviews declare that they have scanned the literature up to a certain point in time, but given that peer review can be a rather lengthy process, a full search for newly appeared literature at the revision stage may be worthwhile. Assessing the contribution of papers that have just appeared is particularly challenging, because there is little perspective with which to gauge their significance and impact on further research and society.

Inevitably, new papers on the reviewed topic (including independently written literature reviews) will appear from all quarters after the review has been published, so that there may soon be the need for an updated review. But this is the nature of science [27] – [32] . I wish everybody good luck with writing a review of the literature.

Acknowledgments

Many thanks to M. Barbosa, K. Dehnen-Schmutz, T. Döring, D. Fontaneto, M. Garbelotto, O. Holdenrieder, M. Jeger, D. Lonsdale, A. MacLeod, P. Mills, M. Moslonka-Lefebvre, G. Stancanelli, P. Weisberg, and X. Xu for insights and discussions, and to P. Bourne, T. Matoni, and D. Smith for helpful comments on a previous draft.

Funding Statement

This work was funded by the French Foundation for Research on Biodiversity (FRB) through its Centre for Synthesis and Analysis of Biodiversity data (CESAB), as part of the NETSEED research project. The funders had no role in the preparation of the manuscript.

Conduct a literature review

What is a literature review.

A literature review is a summary of the published work in a field of study. This can be a section of a larger paper or article, or can be the focus of an entire paper. Literature reviews show that you have examined the breadth of knowledge and can justify your thesis or research questions. They are also valuable tools for other researchers who need to find a summary of that field of knowledge.

Unlike an annotated bibliography, which is a list of sources with short descriptions, a literature review synthesizes sources into a summary that has a thesis or statement of purpose—stated or implied—at its core.

How do I write a literature review?

Step 1: define your research scope.

• What is the specific research question that your literature review helps to define?
• Are there a maximum or minimum number of sources that your review should include?

Ask us if you have questions about refining your topic, search methods, writing tips, or citation management.

Step 2: Identify the literature

Start by searching broadly. Literature for your review will typically be acquired through scholarly books, journal articles, and/or dissertations. Develop an understanding of what is out there, what terms are accurate and helpful, etc., and keep track of all of it with citation management tools . If you need help figuring out key terms and where to search, ask us .

Use citation searching to track how scholars interact with, and build upon, previous research:

• Mine the references cited section of each relevant source for additional key sources
• Use Google Scholar or Scopus to find other sources that have cited a particular work

Step 3: Critically analyze the literature

Key to your literature review is a critical analysis of the literature collected around your topic. The analysis will explore relationships, major themes, and any critical gaps in the research expressed in the work. Read and summarize each source with an eye toward analyzing authority, currency, coverage, methodology, and relationship to other works. The University of Toronto's Writing Center provides a comprehensive list of questions you can use to analyze your sources.

Step 4: Categorize your resources

Divide the available resources that pertain to your research into categories reflecting their roles in addressing your research question. Possible ways to categorize resources include organization by:

• methodology
• theoretical/philosophical approach

Regardless of the division, each category should be accompanied by thorough discussions and explanations of strengths and weaknesses, value to the overall survey, and comparisons with similar sources. You may have enough resources when:

• You've used multiple databases and other resources (web portals, repositories, etc.) to get a variety of perspectives on the research topic.
• The same citations are showing up in a variety of databases.

Additional resources

Undergraduate student resources.

• Literature Review Handout (University of North Carolina at Chapel Hill)
• Learn how to write a review of literature (University of Wisconsin-Madison)

Graduate student and faculty resources

• Information Research Strategies (University of Arizona)
• Literature Reviews: An Overview for Graduate Students (NC State University)
• Oliver, P. (2012). Succeeding with Your Literature Review: A Handbook for Students [ebook]
• Machi, L. A. & McEvoy, B. T. (2016). The Literature Review: Six Steps to Success [ebook]
• Graustein, J. S. (2012). How to Write an Exceptional Thesis or Dissertation: A Step-by-Step Guide from Proposal to Successful Defense [ebook]
• Thomas, R. M. & Brubaker, D. L. (2008). Theses and Dissertations: A Guide to Planning, Research, and Writing

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• Writing Tips

How Long Should a Literature Review Be?

4-minute read

• 7th October 2023

If you’re writing a research paper or dissertation , then you know how important it is to include a thorough, comprehensive literature review. But exactly how long should your literature review be in relation to the rest of your work? While there’s no one-size-fits-all answer to that question, there are some factors that will help determine the length of your review. In this post, we’ll discuss what information to include in your literature review and how long it should be.

Keep reading to learn more.

What Is a Literature Review?

A literature review is a critical summary and evaluation of the current resources (e.g., books and journal articles) on a specific topic or research question. It is a crucial part of academic writing, such as dissertations, in all categories and fields. Essentially, literature reviews help contextualize your investigations and show how your work is building on existing research.

No matter how long your literature review is, it should generally:

●  Establish context for your research (i.e., provide relevant background information so your reader understands the historical significance of your study ).

●  Identify gaps in the existing literature (such as unaddressed questions or aspects of your topic).

●  Highlight significant concepts related to your topic.

●  Cite relevant studies.

●  Support your argument.

It’s also essential that a literature review critically analyze the sources cited in your study, considering factors such as sample size, research design, and potential biases. Be sure to structure your literature review using the same referencing style as the rest of your research paper (e.g., APA , Chicago , MLA ).

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The length of your literature review depends on several factors, including the scope and purpose of your research. In general, the length of the review should be proportionate to your overall paper. For example, if you’re writing a fifty-thousand-word dissertation, then your literature review will likely be an entire chapter comprising about 20 pages. If it’s for a 15-page research paper, your literature review may only be a few pages.

Here are several factors that could affect the length of your literature review:

●  Institutional guidelines : Always check the guidelines provided by your institution or journal (such as an APA journal ). There may be a specific length or word count required for publication.

●  Scope : If your research topic is narrow and focused, your literature review may be shorter. Conversely, if your topic is broad and encompasses a large body of literature, your review may need to be longer.

●  Field of study : Different academic fields may have different expectations regarding the length of literature reviews. For example, literature reviews in the humanities might be longer than those in the natural sciences.

Also, consider your audience. If your literature review is for a general audience or a class assignment, it can probably be shorter and less specialized. However, if it’s for an academic audience in your field of study, you may need to be more thorough and provide an extensive review of the existing literature.

Most literature reviews follow the same basic structure of an introduction, body, and conclusion. Most of the time, they are part of a larger work, so the introduction and conclusion paragraphs will be relatively brief.

However, if the review is a standalone piece, then your introduction and conclusion will be longer since you will need to discuss your research objectives, methods, and findings as well as analyze the literature used in your study.

To ensure your literature review makes an impression, have it professionally proofread by our expert literature review editing services . Submit your free sample of 500 words or less to get started today!

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What is a literature review? [with examples]

What is a literature review?

The purpose of a literature review, how to write a literature review, the format of a literature review, general formatting rules, the length of a literature review, literature review examples, frequently asked questions about literature reviews, related articles.

A literature review is an assessment of the sources in a chosen topic of research.

In a literature review, you’re expected to report on the existing scholarly conversation, without adding new contributions.

If you are currently writing one, you've come to the right place. In the following paragraphs, we will explain:

• the objective of a literature review
• how to write a literature review
• the basic format of a literature review

Tip: It’s not always mandatory to add a literature review in a paper. Theses and dissertations often include them, whereas research papers may not. Make sure to consult with your instructor for exact requirements.

The four main objectives of a literature review are:

• Studying the references of your research area
• Summarizing the main arguments
• Identifying current gaps, stances, and issues
• Presenting all of the above in a text

Ultimately, the main goal of a literature review is to provide the researcher with sufficient knowledge about the topic in question so that they can eventually make an intervention.

The format of a literature review is fairly standard. It includes an:

• introduction that briefly introduces the main topic
• body that includes the main discussion of the key arguments
• conclusion that highlights the gaps and issues of the literature

➡️ Take a look at our guide on how to write a literature review to learn more about how to structure a literature review.

First of all, a literature review should have its own labeled section. You should indicate clearly in the table of contents where the literature can be found, and you should label this section as “Literature Review.”

➡️ For more information on writing a thesis, visit our guide on how to structure a thesis .

There is no set amount of words for a literature review, so the length depends on the research. If you are working with a large amount of sources, it will be long. If your paper does not depend entirely on references, it will be short.

Take a look at these three theses featuring great literature reviews:

• School-Based Speech-Language Pathologist's Perceptions of Sensory Food Aversions in Children [ PDF , see page 20]
• Who's Writing What We Read: Authorship in Criminological Research [ PDF , see page 4]
• A Phenomenological Study of the Lived Experience of Online Instructors of Theological Reflection at Christian Institutions Accredited by the Association of Theological Schools [ PDF , see page 56]

Literature reviews are most commonly found in theses and dissertations. However, you find them in research papers as well.

There is no set amount of words for a literature review, so the length depends on the research. If you are working with a large amount of sources, then it will be long. If your paper does not depend entirely on references, then it will be short.

No. A literature review should have its own independent section. You should indicate clearly in the table of contents where the literature review can be found, and label this section as “Literature Review.”

The main goal of a literature review is to provide the researcher with sufficient knowledge about the topic in question so that they can eventually make an intervention.

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How many references should be included in the bibliography of a Master thesis?

Surprisingly, I have not found a similar question to mine - all I found was a question about the maximum number of citations per sentence.

However, I am more interested in the total number of citations that is considered normal for a paper (to be more specific, a Master Thesis, which in my case will be around 60 pages of content.)

I heard that about 1 - 1.5 multiplied with page count would be a good number of sources cited.

I am asking because I am a little worried that I might have cited too many sources.

• publications

• 2 What is your field? –  Wrzlprmft ♦ Commented Aug 8, 2014 at 11:07
• 15 Cite as many as you have to. Some papers have referred to no references and some have referred to more than fifty or sixty. There is no general rule. –  enthu Commented Aug 8, 2014 at 11:31
• 3 Swedish has a very appropriate word for it: lagom . Just the right amount. –  Davidmh Commented Aug 8, 2014 at 12:41
• 1 A simple example to show why this is not possible to answer: Compare a paper about some original research to a survey about a new field of research. Both of those are perfectly fine to write about, both will get accepted by journals and to some degree you can write master theses about both (well you can, I don't say you should). But the number of citations you'll have for both of those will be at opposite sides of a rather large spectrum. –  Voo Commented Aug 8, 2014 at 16:04
• 4 I might have cited too many sources. — This is simply not possible. The only possible point of concern is whether you've cited each of those sources appropriately . –  JeffE Commented Aug 10, 2014 at 22:24

4 Answers 4

There is no definite answer. It really depends on how much previous literature exists, how much of it you have reviewed and cited appropriately, and (loosely) what the word count of the document is. Page count can misleading, as some theses have many more figures and tables than others.

No one is going to skip to the bibliography, think negative thoughts, and say "you have too many references!" without reading the document. If no individual part of the thesis could be considered as having too many citations, then the thesis as a whole has an appropriate number of citations.

These related questions have answers as to how you can decide if a particular part of the thesis has too many citations.

• Maximum number of citations per sentence?
• Is there such thing as too many references for one paper?

In addition to the other answer, this question is based on some slightly questionable premises, as seen in the sentence "the total number of citations that is considered normal for a paper (to be more specific, a Master Thesis, which in my case will be around 60 pages of content.)":

• In the communities of CS that I am familiar with, a Master Thesis of some 60 pages is not a paper . A paper is usually a document that concisely describes something on typically 5 to 15 pages (depending both on the paper type (short, full, journal, poster abstract, ...) and the layout. Hence, a Master Thesis is not comparable to a paper .
• Papers published in conferences (and maybe to a somewhat lesser extent, in journals) are usually bound to a very strict upper page count limit. When you have lots of interesting stuff to tell, there is only so much space left for references and you often have to skip citing some sources that you would have liked to include. Such a restriction usually doesn't exist in graduation theses such as Bachelor or Master theses. There may be a rough guideline for the expected number of pages, but exceeding that by a moderate amount (in the case you presented, I'd frankly say 80 pages instead of 60 is ok) if the content is worth it is not necessarily a problem - least of all if the extra length is caused by "additional info" such as the appendix or references rather than the core document.
• Lastly, there is no normal number of references because each topic is different. For some Master Thesis tasks, there may be a number of default works that should always be listed in the initial exposition of the general topic, which in itself already fill a page of references, whereas other Master Thesis tasks might not have such a "default list"; the general exposition is done with very few or without any references.

I just completed an M.A. thesis in English literature, and I mean just. I tend to be light on the number of sources I use and I like to have favored sources and work it to exhaustion.

My thesis is about 30,000 words, about 50 percent more than the minimum at my institution. I have 27 secondary sources and six primary sources. The institution requires 20 sources, I don't if that's 20 secondary or 20 total, but what I did will give you and idea what you need to do.

I'm not just out college. In fact, I am senior citizen age. My writing ability is equal to that the people who write the journal article and equal to that of a professional historian too. Reading the journal articles I have had to read to do my seminar papers and my thesis, I have seen many that are excessively heavy on sources. Some are light on sources but seem nevertheless to be good articles.

How you primary sources you cite might depend on your topic. It could be only one. Conceivably, it could be none. For a master's thesis in literature, the minimum might be one secondary source for each thousand word. In imagine, in that case, that it might be double than many for a doctoral disseration. In that case, the number secondary sources for doctoral thesis would have to be around 150.

How many source might depend on the individual and how that persons works their sources. But I would still say, expect to be required to have 150 sources or close to it.

My thesis was low on sources in part because I first outlined a theory and then applied that theory to the characters of four novels without much reference to outside sources.

The number should be N, where N is the exact number of papers that you have really read, understood and (mostly) relevant to your thesis.

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Writing the Literature Review

Barry Mauer and John Venecek

• The Literature Review

What is the Purpose of the Review?

What is the scope of the review, strategies for getting started, types of literature reviews, composition guidelines, how to locate reviews by discipline, key takeaways.

We also provide the following activities:

Types of Literature Reviews [Refresher]

Writing the literature review [refresher], the literature review [1].

Conducting a literary studies research project involves time and effort, with much of it going towards the development of a literature review . A literature review might fill several pages of your research paper and usually appears soon after an introduction but before you present your detailed argument. A literature review provides your audience with an overview of the available research about your area(s) of study, including the literary work, your theory, and methodology. The literature review demonstrates how these scholarly discussions have changed over time, and it allows you to position your research in relation to research that has come before yours. Your aim is to present the discussion up to this point. Depending on the nature of the assignment, you may also include your critical commentary on prior research, noting among this material the weaker and stronger arguments, breakthroughs and dead ends, blind spots and opportunities, the invention of key terms and methods, mistakes as well as misreadings, and so on.

Once you have gathered the research materials you need for your literature review, you have another task: conducting an analysis on the research to see where your original contribution fits into the scholarly conversation. As the saying goes, “we are standing on the shoulders of giants.” Your job is to show a portrait of these giants to your audience, and to show how your work relates to the portrait. On many scholarly topics, literature reviews already exist. You may refer to such existing reviews within your own, indicating any materials might have been overlooked, new developments that have arisen since the publication of the existing literature review, and new perspectives or insights you have about the materials.

Some beginning researchers try to tear down the work of other researchers in an effort to make their own work look good by comparison. It rarely works. First, it tends to make your audience skeptical of your claims. Second, it ignores the fact that even the mistakes, blind spots, and failures of other researchers contribute something to our knowledge. Albert Einstein didn’t disrespect Sir Isaac Newton by saying Newton’s theory of space was wrong and terrible and that Einstein’s own theory was great by comparison. He built upon Newton’s work, showing how it could be improved. If, however, a researcher willfully set out to deceive or distort or to tear down the work of other scholars without good reason, then their work does not deserve such deference.

Most literature reviews appear after the introduction. It presents your reader with relevant information about the scholarly discussion up to now. Later in your paper, you discuss your contribution. Before you begin work on your literature review, let’s discuss what we mean by “literature”; understand the purpose and scope of the review; establish criteria for selecting, organizing, and interpreting your findings; and discuss how to connect your findings to your research question.

Many students seek to “find sources that agree with my claim or idea.” That approach is too narrow, in our view. If we use such an approach, we may get the following results:

• Because we can find sources that agree with almost any claim, readers will wonder whether your claims are weak and the sources are cherry picked.
• While literary scholars sometimes cite authorities to support their claims, they don’t rely only on authority. They respect authority, but not too much. Your own claims need to rely more on evidence (from the literary text, historical and biographical information), and your critical and creative reasoning skills.
• Scholarship is a conversation; thus, the goal is less about finding agreement and more about joining the conversation with the aim of making a valuable contribution to the discussion.

The literature review provides your reader with an overview of the existing research about your topic or problem. It provides the context necessary for your reader to catch up with the scholarly conversation and then to appreciate the value of your contribution to it. The literature review sharpens the focus of your research and demonstrates your knowledge and understanding of the scholarly conversation around your topic, which, in turn, helps establish your credibility as a researcher.

Creating the literature review involves more than gathering citations. It is a qualitative process through which you will discover what is already known about your topic, and identify the key authorities, methods, and theoretical foundations, so you can begin to position your contributions within the scholarly conversation.

Defining the scope of your review will also help you establish criteria to determine the relevance of the sources you are finding. At this stage, you are not reading in-depth; instead, you are skimming through what has already been published and identifying the major concepts, theories, methodologies, and methods present within these published works. You should also be identifying connections, tensions, and contradictions within the already published works of your topic or problem. This involves building on the knowledge of others and understanding what methods, measures, and models we have inherited from previous researchers in our field.

Literature Reviews: Common Errors Made When Conducting a Literature Review [12 min 22 sec]

Video provided courtesy of the Center for Quality Research (CQR)

A literature review helps your reader understand the relationship of your research project to the work of other scholars. It covers the existing knowledge about a problem, and allows you to show the relevance/significance of your contribution to the discussion. Your reader may or may not have read scholarly literature about the theories, methodologies, and literary works you are discussing. But they want to know that you have read it and have thought about it. Your literature review provides not only a summary of the existing scholarship for readers; it also offers your perspective on it.

Begin your work on the literature review by synthesizing the various sources in your annotated bibliography .

For advice on Synthesizing Sources, consider the following from The Purdue Online Writing Lab: [2]

Note that  synthesizing is not the same as summarizing .

• A summary restates the information in one or more sources without providing new insight or reaching new conclusions.
• A synthesis draws on multiple sources to reach a broader conclusion.
• Don’t force a relationship between sources if there isn’t one. Not all of your sources have to complement one another.
• Do your best to highlight the relationships between sources in very clear ways.
• Don’t ignore any outliers in your research. It’s important to take note of every perspective (even those that disagree with your broader conclusions).

Not all humanities research projects contain literature reviews, but many do. Keep in mind that the type of literature review you choose (see list below) pertains to the secondary research – other scholarly sources – and not to the primary literary work. For instance, a literature review about Kate Chopin’s writing will be your thoughts about the scholarship on Chopin and not about Chopin’s text itself. You are summarizing what you see in the scholarly literature about Chopin’s writing. The literature review puts you in the position of authority not just on Chopin’s writing but on the scholarship about her writing. You are seeking to understand what scholars have said about her work. Scholars might belong to different schools of thought (psychoanalytic, feminist, Marxist, etc.). They might make different arguments about Chopin. They might use different methodological approaches. 

If your research involves two or more theories, such as psychology and genre studies, you may need to create multiple literature reviews, one for each theory or methodology. If the theories overlap with each other significantly (i.e., Marxism and Cultural Studies), you may combine them. Your literature review need not include everything about the subject area – you would need to write a book to cover a single theory – but only those concepts and methods that are most relevant to your research problem.

Factors to Consider When Developing Your Literature Review

• Determine the Scope : How broad or narrow should your literature review be? You may want to focus on recent scholarship only, or on a particular school of thought in the literature. Your scope is determined by your purpose; what is it you aim to achieve with your research?
• Establish Criteria : We discussed the importance of defining the purpose and scope of your review on the previous page, but it’s worth reviewing here as well. This step will help you establish important criteria and focus your searching. For example, how many sources will you need? What types of sources (primary, secondary, statistics, media)? Is currency important? Do you know who the prominent authors or theorists are in your subject area? Take some time to map out these or other important factors before you begin searching journals and databases.
• Consider Your Audience : Unlike a work cited page or an annotated bibliography, both of which are lists of sources, a literature review is essayistic and can be considered a precursor to your final paper. Therefore, it should be written in your own voice, and it should be geared toward a specific audience. Considering audience during this early stage will help focus your final paper as well.
• Find Models : We’ll discuss the different types of literature reviews and how to locate examples in the section below. However, even if you’re undecided about what type of review will work best for you, you may want to review some example literature reviews to get a sense of what they look like before you begin your own.

One piece of advice before starting: look for existing literature reviews on your area of scholarship. You can build on the work that other scholars have put into reviewing the scholarly literature. There’s no need to completely “reinvent the wheel” if some of the work is already done.

Scholars sometimes publish “stand-alone” literature reviews that are not part of a larger work; such literature reviews are valuable contributions to the field, as they summarize the state of knowledge for other scholars.

Maria J. Grant and Andrew Booth’s “A Typology of Reviews” identifies 14 distinct types of literature reviews. Further, the UCLA library created a chart to complement the article and for easy comparison of those 14 types of reviews. This section provides a brief summary of the most common literature reviews. For a more complete analysis, please see the full article and the chart .

To choose the most appropriate structure, put yourself in your reader’s shoes and think through their need for information. The literature review is about providing context for your contribution. How much context do people need? Keep it to the minimum necessary; compressing a lot of information into a small amount of text is a must.

These structures are not meant to be straightjackets but tools to help you organize your research. If you find that the tool is working, then keep using it. If not, switch tools or modify the one you are using. Keep in mind that the types of literature reviews are just different ways of organizing information. So, you can discuss literary trends without organizing your review of secondary literature by trend; your discussion can be organized by theory or theme, for examples. In our literature reviews, we are not recounting other scholars’ arguments at length but merely providing key concepts so we can summarize the discussion so far and position our own claims. You don’t have to adhere strictly to one structure or another. They are just organizing tools that help you manage your material (and help your reader make sense of it).

Types of Reviews

• Traditional or narrative reviews : This approach will generate a comprehensive, critical analysis of the published research on your topic. However, rather than merely compiling as many sources as possible, use this approach to establish a theoretical framework for your paper, establish trends, and identify gaps in the research. This process should bring your research question into clearer focus and help define a thesis that you will argue for in your paper. This is perhaps the most common and general type of literature review. The examples listed below are all designed to serve a more specific purpose.
• Argumentative : The purpose of an argumentative literature review is to select sources for the purpose of supporting or refuting a specific claim. While this type of review can help the author make a strong case for or against an issue, they can also be prone to claims of bias. Later in this textbook, we will read about the distinction between warranted and unwarranted bias . One is ok and the other is not.
• Chronological : A chronological review is used when the author wants to demonstrate the progression of how a theory, methodology, or issue has progressed over time. This method is most effective when there is a clear chronological path to the research about a specific historical event or trend as opposed to a more recursive theoretical concept.
• By trend : This is similar to the chronological approach except it focuses on clearly-defined trends rather than date ranges. This would be most appropriate if you want to illustrate changing perspectives or attitudes about a given issue when specific date ranges are less important than the ebb and flow of the trend.
• Thematic : In this type of literature review, the author will select specific themes that he or she feels are important to understanding a larger topic or concept. Then, the author will organize the sources around those themes, which are often based on relevance or importance. The value of this method is that the process of organizing the review by theme is similar to constructing an argument. This can help the author see how resources connect to each other and determine how as well as why specific sources support their thesis.
• Theoretical : The goal of this type of review is to examine how theory has shaped the research on a given topic. It establishes existing theoretical models, their connections, and how extensively they have been developed in the published research. For example, Jada applied critical race theory to her analysis of Sonny’s Blues , but she might also consider conducting a more comprehensive review of other theoretical frameworks such as feminism, Marxism, or postmodernism. Doing so could provide insight into alternate readings, and help her identify theoretical gaps such as unexplored or under-developed approaches to Baldwin’s work.
• Methodological : The approach focuses on the various methodologies used by researchers in a specific area rather than an analysis of their findings. In this case, you would create a framework of approaches to data collection related to your topic or research question. This is perhaps more common in education or the social and hard sciences where published research often includes a methods section, but it is sometimes appropriate for the digital humanities as well.
• Scoping : The aim of a scoping review is to provide a comprehensive overview or map of the published research or evidence related to a research question. This might be considered a prelude to a systematic review that would take the scoping review one step further toward answering a clearly defined research question. See below for more details.
• Systematic : The systematic review is most appropriate when you have a clearly-defined research question and have established criteria for the types of sources you need. In this way, the systematic review is less exploratory than other types of reviews. Rather, it is comprehensive, strategic, and focused on answering a specific research question. For this reason, the systematic review is more common in the health and social sciences, where comprehensiveness is more important. Literature reviews in the Humanities are not usually exhaustive but tend to show only the most representative or salient developments in the scholarship.
• Meta-analysis : Does your research deal with statistics or large amounts of data? If so, then a meta-analysis might be best for you rather than providing a critical review, the meta-analysis will summarize and synthesize the results of numerous studies that involve statistics or data to provide a more comprehensive picture than would be possible from just one study.

An argumentative literature review presents and takes sides in scholarly arguments about the literary work. It makes arguments about other scholars’ work. It does not necessarily involve a claim that the literary work is itself making an argument. Likewise, a chronological literature review presents the scholarly literature in chronological order.

You don’t need to keep strictly to one type. Scholars often combine features from various types of literature reviews. A sample review that combines the follow types –

• Argumentative
• Theoretical
• Methodological

– is the excellent work of Eiranen, Reetta, Mari Hatavara, Ville Kivimäki, Maria Mäkelä & Raisa Maria Toivo (2022) “ Narrative and Experience: Interdisciplinary Methodologies between History and Narratology , ” Scandinavian Journal of History , 47:1, 1-15

When writing your literature review, please follow these pointers:

• Conduct systematic searches
• Use Evidence
• Be Selective
• Use Quotes Sparingly
• Summarize & Synthesize
• Use Caution when Paraphrasing
• Use Your Own Voice

Advice from James Mason University’s “Literature Reviews: An Overview”

A note on synthesizing : Don’t make the common mistake of summarizing individual studies or articles one after the other. The goal is to synthesize — that is, to make observations about groups of studies. Synthesis often uses language like this:

• Much of the literature on [topic x ] focuses on [major themes].
• In recent years, researchers have begun investigating [facets a , b , and c ] of [topic x ].
• The studies in this review of [topic x ] confirm / suggest / call into question / support [idea / practice / finding / method / theory / guideline y ].
• In the reviewed studies [variable x ] was generally associated with higher / lower rates of [outcome y ].
• A limitation of some / most / all of these studies is [ y ].

Please see this sample annotated literature review  from James Mason University.

Structure of a literature review [2]

• Problematization: The 2 to 3 pages of problematization are a distinct, iterative, step. It may take doing such a statement a few times before moving forward to writing the actual paper.
• Search: Write down your keyword sets, your updated keyword sets, and databases. It is perfectly within a reviewer’s rights to ask for these details.
• Summary: Really getting to know major themes requires some annotation of articles. You want to identify core papers and themes and write about them. This helps you really learn the material. [ChatGPT or Wikipedia are no substitute for deep engagement with a paper.]
• Argument: Either outline or create a slide deck that help you express the arguments in your paper. Read them out loud. Have friends look at them. Present them. [Every literature review has an argument. If not, it’s a summary. A summary does not merit publication in a top outlet.]
• Unpacking: Once you’ve nailed the short pitch, unpack the full argument. [ a) Take time in each major section to map out a) the argument, b) the supporting evidence, and the takeaway. b) Take those major sections, reconcile them, make sure they don’t overlap, then move on to writing. c) Sketch out the paper’s sections, tables, figures, and appendices.]
• Writing: Writing is the easy part. You can always put words to the screen. [Revising and improving is hard. Make time to write every day. Improving requires feedback. Find a writing partner to give feedback. Create your tables and figures. Write to them. Make sure the words in the paper align to the visuals.]
• Communicate: When the paper is done, go back and create a paper presentation. [I do this for the papers that I’m most serious about. The act of storyboarding helps me sort out the small pieces of the story that don’t fit together. If I really want it to succeed, I present it. The act of presenting helps me get it right. My best papers sometimes take seven or eight presentations to get it right. Then I return to the paper and fine tune it. Only then, does it have a shot at a top outlet.]

Literature reviews can be published as part of a scholarly article, often after the introduction and sometimes with a header, but they can also be published as a standalone essay. To find examples of what reviews look like in your discipline, choose an appropriate subject database (such as MLA for literary criticism) and conduct a keyword search with the term “Literature Review” added in quotes:

Not only do these examples demonstrate how to structure different types of literature reviews, but some offer insights into trends and directions for future research. In the next section, we’ll take a closer look at some reading strategies to help guide you through this process.

Since scholars already have produced literature reviews on various scholarly conversations, you don’t always need to “reinvent the wheel” (start a literature review from nothing). You can find a published literature review and update it or amend it; scholars do that all the time. However, you must properly cite work you incorporate from others.

• What types of literature review will you be using for your paper? Why did you make this selection over others? If you haven’t made a selection yet, which types are you considering?
• What specific challenges do you face in following a literature review structure?
• If there are any elements of your assignment that need clarification, please list them.
• What was the most important lesson you learned from this page? What point was confusing or difficult to understand?
• In the “Back Matter” of this book, you will find a page titled “Rubrics.” On that page, we provide a rubric for Creating a Literature Review ↵
• Richard West, Brigham Young University, amended by Jason Thatcher, Temple University - https://www.linkedin.com/posts/jason-thatcher-0329764_academicwriting-topten2023-activity-7146507675021766656-BB0O ↵

Writing the Literature Review Copyright © 2021 by Barry Mauer and John Venecek is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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• http://orcid.org/0000-0003-0157-5319 Ahtisham Younas 1 , 2 ,
• http://orcid.org/0000-0002-7839-8130 Parveen Ali 3 , 4
• 1 Memorial University of Newfoundland , St John's , Newfoundland , Canada
• 2 Swat College of Nursing , Pakistan
• 3 School of Nursing and Midwifery , University of Sheffield , Sheffield , South Yorkshire , UK
• 4 Sheffield University Interpersonal Violence Research Group , Sheffield University , Sheffield , UK
• Correspondence to Ahtisham Younas, Memorial University of Newfoundland, St John's, NL A1C 5C4, Canada; ay6133{at}mun.ca

https://doi.org/10.1136/ebnurs-2021-103417

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Introduction

Literature reviews offer a critical synthesis of empirical and theoretical literature to assess the strength of evidence, develop guidelines for practice and policymaking, and identify areas for future research. 1 It is often essential and usually the first task in any research endeavour, particularly in masters or doctoral level education. For effective data extraction and rigorous synthesis in reviews, the use of literature summary tables is of utmost importance. A literature summary table provides a synopsis of an included article. It succinctly presents its purpose, methods, findings and other relevant information pertinent to the review. The aim of developing these literature summary tables is to provide the reader with the information at one glance. Since there are multiple types of reviews (eg, systematic, integrative, scoping, critical and mixed methods) with distinct purposes and techniques, 2 there could be various approaches for developing literature summary tables making it a complex task specialty for the novice researchers or reviewers. Here, we offer five tips for authors of the review articles, relevant to all types of reviews, for creating useful and relevant literature summary tables. We also provide examples from our published reviews to illustrate how useful literature summary tables can be developed and what sort of information should be provided.

Tip 1: provide detailed information about frameworks and methods

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Tabular literature summaries from a scoping review. Source: Rasheed et al . 3

The provision of information about conceptual and theoretical frameworks and methods is useful for several reasons. First, in quantitative (reviews synthesising the results of quantitative studies) and mixed reviews (reviews synthesising the results of both qualitative and quantitative studies to address a mixed review question), it allows the readers to assess the congruence of the core findings and methods with the adapted framework and tested assumptions. In qualitative reviews (reviews synthesising results of qualitative studies), this information is beneficial for readers to recognise the underlying philosophical and paradigmatic stance of the authors of the included articles. For example, imagine the authors of an article, included in a review, used phenomenological inquiry for their research. In that case, the review authors and the readers of the review need to know what kind of (transcendental or hermeneutic) philosophical stance guided the inquiry. Review authors should, therefore, include the philosophical stance in their literature summary for the particular article. Second, information about frameworks and methods enables review authors and readers to judge the quality of the research, which allows for discerning the strengths and limitations of the article. For example, if authors of an included article intended to develop a new scale and test its psychometric properties. To achieve this aim, they used a convenience sample of 150 participants and performed exploratory (EFA) and confirmatory factor analysis (CFA) on the same sample. Such an approach would indicate a flawed methodology because EFA and CFA should not be conducted on the same sample. The review authors must include this information in their summary table. Omitting this information from a summary could lead to the inclusion of a flawed article in the review, thereby jeopardising the review’s rigour.

Tip 2: include strengths and limitations for each article

Critical appraisal of individual articles included in a review is crucial for increasing the rigour of the review. Despite using various templates for critical appraisal, authors often do not provide detailed information about each reviewed article’s strengths and limitations. Merely noting the quality score based on standardised critical appraisal templates is not adequate because the readers should be able to identify the reasons for assigning a weak or moderate rating. Many recent critical appraisal checklists (eg, Mixed Methods Appraisal Tool) discourage review authors from assigning a quality score and recommend noting the main strengths and limitations of included studies. It is also vital that methodological and conceptual limitations and strengths of the articles included in the review are provided because not all review articles include empirical research papers. Rather some review synthesises the theoretical aspects of articles. Providing information about conceptual limitations is also important for readers to judge the quality of foundations of the research. For example, if you included a mixed-methods study in the review, reporting the methodological and conceptual limitations about ‘integration’ is critical for evaluating the study’s strength. Suppose the authors only collected qualitative and quantitative data and did not state the intent and timing of integration. In that case, the strength of the study is weak. Integration only occurred at the levels of data collection. However, integration may not have occurred at the analysis, interpretation and reporting levels.

Tip 3: write conceptual contribution of each reviewed article

While reading and evaluating review papers, we have observed that many review authors only provide core results of the article included in a review and do not explain the conceptual contribution offered by the included article. We refer to conceptual contribution as a description of how the article’s key results contribute towards the development of potential codes, themes or subthemes, or emerging patterns that are reported as the review findings. For example, the authors of a review article noted that one of the research articles included in their review demonstrated the usefulness of case studies and reflective logs as strategies for fostering compassion in nursing students. The conceptual contribution of this research article could be that experiential learning is one way to teach compassion to nursing students, as supported by case studies and reflective logs. This conceptual contribution of the article should be mentioned in the literature summary table. Delineating each reviewed article’s conceptual contribution is particularly beneficial in qualitative reviews, mixed-methods reviews, and critical reviews that often focus on developing models and describing or explaining various phenomena. Figure 2 offers an example of a literature summary table. 4

Tabular literature summaries from a critical review. Source: Younas and Maddigan. 4

Tip 4: compose potential themes from each article during summary writing

While developing literature summary tables, many authors use themes or subthemes reported in the given articles as the key results of their own review. Such an approach prevents the review authors from understanding the article’s conceptual contribution, developing rigorous synthesis and drawing reasonable interpretations of results from an individual article. Ultimately, it affects the generation of novel review findings. For example, one of the articles about women’s healthcare-seeking behaviours in developing countries reported a theme ‘social-cultural determinants of health as precursors of delays’. Instead of using this theme as one of the review findings, the reviewers should read and interpret beyond the given description in an article, compare and contrast themes, findings from one article with findings and themes from another article to find similarities and differences and to understand and explain bigger picture for their readers. Therefore, while developing literature summary tables, think twice before using the predeveloped themes. Including your themes in the summary tables (see figure 1 ) demonstrates to the readers that a robust method of data extraction and synthesis has been followed.

Tip 5: create your personalised template for literature summaries

Often templates are available for data extraction and development of literature summary tables. The available templates may be in the form of a table, chart or a structured framework that extracts some essential information about every article. The commonly used information may include authors, purpose, methods, key results and quality scores. While extracting all relevant information is important, such templates should be tailored to meet the needs of the individuals’ review. For example, for a review about the effectiveness of healthcare interventions, a literature summary table must include information about the intervention, its type, content timing, duration, setting, effectiveness, negative consequences, and receivers and implementers’ experiences of its usage. Similarly, literature summary tables for articles included in a meta-synthesis must include information about the participants’ characteristics, research context and conceptual contribution of each reviewed article so as to help the reader make an informed decision about the usefulness or lack of usefulness of the individual article in the review and the whole review.

In conclusion, narrative or systematic reviews are almost always conducted as a part of any educational project (thesis or dissertation) or academic or clinical research. Literature reviews are the foundation of research on a given topic. Robust and high-quality reviews play an instrumental role in guiding research, practice and policymaking. However, the quality of reviews is also contingent on rigorous data extraction and synthesis, which require developing literature summaries. We have outlined five tips that could enhance the quality of the data extraction and synthesis process by developing useful literature summaries.

• Aromataris E ,
• Rasheed SP ,

Twitter @Ahtisham04, @parveenazamali

Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

Competing interests None declared.

Patient consent for publication Not required.

Provenance and peer review Not commissioned; externally peer reviewed.

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Ethiopia Population 2024 (Live)

Ethiopia ’s current population is about 115 million and is expected to surpass 200 million by the end of 2049. Ethiopia’s population is growing about 2.7% annually with no projected peak year or period of decline.

The birth rate in Ethiopia is 36 births per 1,000 people. The fertility rate is 4.1 births per woman. Religion plays a major role in Ethiopia’s high birth rate, as well as the lack of contraceptives.

The disproportionate population increase has hindered the economy’s ability to grow and develop at a more rapid pace due to the increased need for more resources. Ethiopia remains one of the poorest countries in the world due to its rapid population upsurge.

Ethiopia Population Growth

Ethiopia is a nation that has been beset by hunger and poverty for most of its long history. A land where child starvation and subsequent death have been prevalent for such a long time requires assistance from the more privileged and prosperous nations of the world. It is the responsibility of all members of the peaceful international community to step in with more rigor and determination to empower the Ethiopians. This population has proven to be one of the strongest on the face of the earth, having endured massive hardships. If it is given a little assistance, Ethiopia will be able to build on the strength of its inhabitants in order to increase the strength of the nation itself.

Ethiopia Population Projections

Ethiopia is currently one of the fastest growing countries in the world, with a growth rate of 3.02% per year. If Ethiopia follows its current rate of growth, its population will double in the next 30 years, hitting 210 million by 2060. Most of the world's population growth in the next 40-50 years is expected to come from Africa , and Ethiopia will be a large part of the growth.

Ethiopia Growth Rate

Ethiopia population clock.

Net increase of 1 person every 9 seconds

Population estimates based on interpolation of data from World Population Prospects

Components of Population Change

Ethiopia Population Density Map

Ethiopia Area and Population Density

The surface area in Ethiopia is currently at 1,104,300 km² (or 426,372.6137 miles square). Ethiopia has a population density of 83 people per square mile (214/square mile), which ranks 123rd in the world.

Largest Cities in Ethiopia

The largest city and capital of Ethiopia is Addis Ababa , or Addis Abeba, which has an estimated population of 3.6 million in the city proper and a metro population of more than 4.6 million. Being as old as two millenniums, its cultures and traditions hold family as a significant part of Ethiopian life, sometimes even surpassing the significance their careers or businesses might have.

Other major cities include Adama (324,000), Gondar (324,000), Mek'ele (324,000), and Hawassa (302,000).

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Ethiopia Population by Year (Historical)

Ethiopia Population by Year (Projections)

Ethiopia population pyramid 2024, ethiopia median age, ethiopia population by age.

There are people over age 18 in Ethiopia .

Census Years

Ethiopia Population Pyramid

With one of the highest poverty levels in the world, Ethiopia is considered by many to be one of the most under-developed nations in the world. But within its African boundaries lies a nation filled with a rich culture and heritage. Bordered by Kenya , South Sudan , Sudan , Djibouti , Eritrea , and Somalia .

Ethiopia is the most populous landlocked country in the continent of Africa and the second-most populous country of Africa after Nigeria . This estimate of how many people live in Ethiopia is based on the most recent United Nations projections, and makes Ethiopia the 14th most populous country in the world. The most recent census in 2007 found an official population of 73.7 million.

Ethiopia Demographics

Ethiopia is home to various ethnicities, predominantly the Oromo at 34.4% of the country's population and the Amhara, who account for 27% of the population. Other major ethnic groups include the Somali (6.2%), Tigray (6.1%), Sidama (4%), Gurage (2.5%), Welayta (2.3%), Afar (1.7%), Hadiya (1.7%), and Gamo (1.5%).

In 2009, Ethiopia had an estimated 135,000 asylum seekers and refugees, mostly from Somalia (64,000), Eritrea (42,000) and Sudan (23,000). The government requires refugees to live in designated refugee camps. According to a 2013 report, the number of refugees hosted by Ethiopia has grown to 680,000.

Ethiopia Religion, Economy and Politics

Ethiopia has close ties with all three major Abrahamic religions, and it was the first in the region to officially adopt Christianity in the 4th century. Christians account for 63% of the country's population, with 44% belonging to the Ethiopian Orthodox Church. Ethiopia has the first Hijra in Islamic history and the oldest Muslim settlement on the continent. Muslims account for 34% of the population.

Despite its wealth in culture, Ethiopia, unfortunately, does not suffer the same fate economically. With a significantly agriculture-based economy, it is not surprising that in today's technologically thriving world, Ethiopia has one of the lowest incomes per capita. Its reliance on domestic investment restricts foreign investment, which could otherwise account for a comparatively successful economy. However, improvement in agricultural practices has shown a decrease in the level of starvation that the country had been previously accustomed to. The GDP is also increasing, showing a 7% increase in 2014. The composition of the labor force is almost 40%, accounting for another step toward progress. However, only if the conditions of the average Ethiopian get better will the country be able to witness a better tomorrow.

The median age in Ethiopia is approximately 17.9 years of age. 60% of the population in Ethiopia is under the age of 25.

In terms of access to clean drinking water and sanitation, the numbers are still quite grim in this country. According to the World Factbook, only 57% of the country has improved access to clean drinking water, while 42% still struggle to find clean water. Only 28% of the population has access to improved sanitation services, while 72% struggle to maintain sanitation. This likely contributes greatly to the very high degree of risk with transmittable diseases and illnesses in the area.

Only 49% of the population over 15 years of age is literate and many children only attend school for 8 or 9 years.

Ethiopia Population History

The conditions of poverty entail deterioration in health for many of Ethiopia's inhabitants. The most common diseases that cause mortality among many Ethiopians are AIDS, tuberculosis, malaria, and various communicable diseases that occur due to improper sanitation and malnutrition. Most women give birth to children outside of the vicinity of hospitals. Often the mothers are only attended to by an elderly midwife. The mortality rate of mothers while giving birth is high. Various organizations, governmental and non-governmental, seek to improve the deplorable health conditions in Ethiopia. The World Health Organization is working to initiate a healthy Ethiopia. Low literacy levels also support the inferior health conditions. Therefore, it is important to provide the Ethiopians with adequate knowledge regarding common diseases and their appropriate medication and cure. The empowerment of women could also help achieve improvements in the circumstances pertaining to the well-being of Ethiopians.

• National Bank of Ethiopia
• World Population Prospects (2024 Revision) - United Nations population estimates and projections.

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Strengthening akis for sustainable agricultural features: insights and innovations from the european unio: a literature review.

1. Introduction

2. materials and methods, 2.1. data collection procedure, 2.2. identification criteria, 2.3. screening and selection criteria, 2.4. eligibility and inclusion criteria.

• The studies that were carried out or considered the 28 countries in the European Union (including the United Kingdom until 2019 and excluding Romania).
• Studies published in the English Language.
• Studies that were published within the past 11 years (the review covers the period from 2014 to 2024, a period in which the two previous Programming Periods of the Common Agricultural Policy were implemented).
• Studies covering the inclusion of a transparent description of the process of data acquisition and interpretation.
• Studies covering a primary or secondary class investigation on the subject matter.
• Studies showcasing the effects of AKISs and FASs on agricultural knowledge advancement.
• Studies published in a non-English language.
• Studies carried out outside the EU.
• Studies with unclear methodology of data collection and analysis.
• Studies lacking author names and affiliation.
• Studies not covering both the main issues of this review (i.e., AKIS and FAS).

4. Discussion

4.1. akis and fas in the foreground through the new cap, 4.2. improving the effectiveness of an akis, 5. conclusions, author contributions, institutional review board statement, data availability statement, conflicts of interest.

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Kountios, G.; Kanakaris, S.; Moulogianni, C.; Bournaris, T. Strengthening AKIS for Sustainable Agricultural Features: Insights and Innovations from the European Unio: A Literature Review. Sustainability 2024 , 16 , 7068. https://doi.org/10.3390/su16167068

Kountios G, Kanakaris S, Moulogianni C, Bournaris T. Strengthening AKIS for Sustainable Agricultural Features: Insights and Innovations from the European Unio: A Literature Review. Sustainability . 2024; 16(16):7068. https://doi.org/10.3390/su16167068

Kountios, Georgios, Spyridon Kanakaris, Christina Moulogianni, and Thomas Bournaris. 2024. "Strengthening AKIS for Sustainable Agricultural Features: Insights and Innovations from the European Unio: A Literature Review" Sustainability 16, no. 16: 7068. https://doi.org/10.3390/su16167068

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• Research article
• Open access
• Published: 15 August 2024

The impact of adverse childhood experiences on multimorbidity: a systematic review and meta-analysis

• Dhaneesha N. S. Senaratne 1 ,
• Bhushan Thakkar 1 ,
• Blair H. Smith 1 ,
• Tim G. Hales 2 ,
• Louise Marryat 3 &
• Lesley A. Colvin 1  

BMC Medicine volume  22 , Article number:  315 ( 2024 ) Cite this article

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Adverse childhood experiences (ACEs) have been implicated in the aetiology of a range of health outcomes, including multimorbidity. In this systematic review and meta-analysis, we aimed to identify, synthesise, and quantify the current evidence linking ACEs and multimorbidity.

We searched seven databases from inception to 20 July 2023: APA PsycNET, CINAHL Plus, Cochrane CENTRAL, Embase, MEDLINE, Scopus, and Web of Science. We selected studies investigating adverse events occurring during childhood (< 18 years) and an assessment of multimorbidity in adulthood (≥ 18 years). Studies that only assessed adverse events in adulthood or health outcomes in children were excluded. Risk of bias was assessed using the ROBINS-E tool. Meta-analysis of prevalence and dose–response meta-analysis methods were used for quantitative data synthesis. This review was pre-registered with PROSPERO (CRD42023389528).

From 15,586 records, 25 studies were eligible for inclusion (total participants = 372,162). The prevalence of exposure to ≥ 1 ACEs was 48.1% (95% CI 33.4 to 63.1%). The prevalence of multimorbidity was 34.5% (95% CI 23.4 to 47.5%). Eight studies provided sufficient data for dose–response meta-analysis (total participants = 197,981). There was a significant dose-dependent relationship between ACE exposure and multimorbidity ( p  < 0.001), with every additional ACE exposure contributing to a 12.9% (95% CI 7.9 to 17.9%) increase in the odds for multimorbidity. However, there was heterogeneity among the included studies ( I 2  = 76.9%, Cochran Q  = 102, p  < 0.001).

Conclusions

This is the first systematic review and meta-analysis to synthesise the literature on ACEs and multimorbidity, showing a dose-dependent relationship across a large number of participants. It consolidates and enhances an extensive body of literature that shows an association between ACEs and individual long-term health conditions, risky health behaviours, and other poor health outcomes.

Peer Review reports

In recent years, adverse childhood experiences (ACEs) have been identified as factors of interest in the aetiology of many conditions [ 1 ]. ACEs are potentially stressful events or environments that occur before the age of 18. They have typically been considered in terms of abuse (e.g. physical, emotional, sexual), neglect (e.g. physical, emotional), and household dysfunction (e.g. parental separation, household member incarceration, household member mental illness) but could also include other forms of stress, such as bullying, famine, and war. ACEs are common: estimates suggest that 47% of the UK population have experienced at least one form, with 12% experiencing four or more [ 2 ]. ACEs are associated with poor outcomes in a range of physical health, mental health, and social parameters in adulthood, with greater ACE burden being associated with worse outcomes [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ].

Over a similar timescale, multimorbidity has emerged as a significant heath challenge. It is commonly defined as the co-occurrence of two or more long-term conditions (LTCs), with a long-term condition defined as any physical or mental health condition lasting, or expected to last, longer than 1 year [ 9 ]. Multimorbidity is both common and age-dependent, with a global adult prevalence of 37% that rises to 51% in adults over 60 [ 10 , 11 ]. Individuals living with multimorbidity face additional challenges in managing their health, such as multiple appointments, polypharmacy, and the lack of continuity of care [ 12 , 13 , 14 ]. Meanwhile, many healthcare systems struggle to manage the additional cost and complexity of people with multimorbidity as they have often evolved to address the single disease model [ 15 , 16 ]. As global populations continue to age, with an estimated 2.1 billion adults over 60 by 2050, the pressures facing already strained healthcare systems will continue to grow [ 17 ]. Identifying factors early in the aetiology of multimorbidity may help to mitigate the consequences of this developing healthcare crisis.

Many mechanisms have been suggested for how ACEs might influence later life health outcomes, including the risk of developing individual LTCs. Collectively, they contribute to the idea of ‘toxic stress’; cumulative stress during key developmental phases may affect development [ 18 ]. ACEs are associated with measures of accelerated cellular ageing, including changes in DNA methylation and telomere length [ 19 , 20 ]. ACEs may lead to alterations in stress-signalling pathways, including changes to the immune, endocrine, and cardiovascular systems [ 21 , 22 , 23 ]. ACEs are also associated with both structural and functional differences in the brain [ 24 , 25 , 26 , 27 ]. These diverse biological changes underpin psychological and behavioural changes, predisposing individuals to poorer self-esteem and risky health behaviours, which may in turn lead to increased risk of developing individual LTCs [ 1 , 2 , 28 , 29 , 30 , 31 , 32 ]. A growing body of evidence has therefore led to an increased focus on developing trauma-informed models of healthcare, in which the impact of negative life experiences is incorporated into the assessment and management of LTCs [ 33 ].

Given the contributory role of ACEs in the aetiology of individual LTCs, it is reasonable to suspect that ACEs may also be an important factor in the development of multimorbidity. Several studies have implicated ACEs in the aetiology of multimorbidity, across different cohorts and populations, but to date no meta-analyses have been performed to aggregate this evidence. In this review, we aim to summarise the state of the evidence linking ACEs and multimorbidity, to quantify the strength of any associations through meta-analysis, and to highlight the challenges of research in this area.

Search strategy and selection criteria

We conducted a systematic review and meta-analysis that was prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO) on 25 January 2023 (ID: CRD42023389528) and reported using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

We developed a search strategy based on previously published literature reviews and refined it following input from subject experts, an academic librarian, and patient and public partners (Additional File 1: Table S1). We searched the following seven databases from inception to 20 July 2023: APA PsycNET, CINAHL Plus, Cochrane CENTRAL, Embase, MEDLINE, Scopus, and Web of Science. The search results were imported into Covidence (Veritas Health Innovation, Melbourne, Australia), which automatically identified and removed duplicate entries. Two reviewers (DS and BT) independently performed title and abstract screening and full text review. Discrepancies were resolved by a third reviewer (LC).

Reports were eligible for review if they included adults (≥ 18 years), adverse events occurring during childhood (< 18 years), and an assessment of multimorbidity or health status based on LTCs. Reports that only assessed adverse events in adulthood or health outcomes in children were excluded.

The following study designs were eligible for review: randomised controlled trials, cohort studies, case–control studies, cross-sectional studies, and review articles with meta-analysis. Editorials, case reports, and conference abstracts were excluded. Systematic reviews without a meta-analysis and narrative synthesis review articles were also excluded; however, their reference lists were screened for relevant citations.

Data analysis

Two reviewers (DS and BT) independently performed data extraction into Microsoft Excel (Microsoft Corporation, Redmond, USA) using a pre-agreed template. Discrepancies were resolved by consensus discussion with a third reviewer (LC). Data extracted from each report included study details (author, year, study design, sample cohort, sample size, sample country of origin), patient characteristics (age, sex), ACE information (definition, childhood cut-off age, ACE assessment tool, number of ACEs, list of ACEs, prevalence), multimorbidity information (definition, multimorbidity assessment tool, number of LTCs, list of LTCs, prevalence), and analysis parameters (effect size, model adjustments). For meta-analysis, we extracted ACE groups, number of ACE cases, number of multimorbidity cases, number of participants, odds ratios or regression beta coefficients, and 95% confidence intervals (95% CI). Where data were partially reported or missing, we contacted the study authors directly for further information.

Two reviewers (DS and BT) independently performed risk of bias assessments of each included study using the Risk Of Bias In Non-randomized Studies of Exposures (ROBINS-E) tool [ 34 ]. The ROBINS-E tool assesses the risk of bias for the study outcome relevant to the systematic review question, which may not be the primary study outcome. It assesses risk of bias across seven domains; confounding, measurement of the exposure, participant selection, post-exposure interventions, missing data, measurement of the outcome, and selection of the reported result. The overall risk of bias for each study was determined using the ROBINS-E algorithm. Discrepancies were resolved by consensus discussion.

All statistical analyses were performed in R version 4.2.2 using the RStudio integrated development environment (RStudio Team, Boston, USA). To avoid repetition of participant data, where multiple studies analysed the same patient cohort, we selected the study with the best reporting of raw data for meta-analysis and the largest sample size. Meta-analysis of prevalence was performed with the meta package [ 35 ], using logit transformations within a generalised linear mixed model, and reporting the random-effects model [ 36 ]. Inter-study heterogeneity was assessed and reported using the I 2 statistic, Cochran Q statistic, and Cochran Q p -value. Dose–response meta-analysis was performed using the dosresmeta package [ 37 ] following the method outlined by Greenland and Longnecker (1992) [ 38 , 39 ]. Log-linear and non-linear (restricted cubic spline, with knots at 5%, 35%, 65%, and 95%) random effects models were generated, and goodness of fit was evaluated using a Wald-type test (denoted by X 2 ) and the Akaike information criterion (AIC) [ 39 ].

Patient and public involvement

The Consortium Against Pain Inequality (CAPE) Chronic Pain Advisory Group (CPAG) consists of individuals with lived experiences of ACEs, chronic pain, and multimorbidity. CPAG was involved in developing the research question. The group has experience in systematic review co-production (in progress).

The search identified 15,586 records, of which 25 met inclusion criteria for the systematic review (Fig.  1 ) [ 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 ]. The summary characteristics can be found in Additional File 1: Table S2. Most studies examined European ( n  = 11) or North American ( n  = 9) populations, with a few looking at Asian ( n  = 3) or South American ( n  = 1) populations and one study examining a mixed cohort (European and North American populations). The total participant count (excluding studies performed on the same cohort) was 372,162. Most studies had a female predominance (median 53.8%, interquartile range (IQR) 50.9 to 57.4%).

Flow chart of selection of studies into the systematic review and meta-analysis. Flow chart of selection of studies into the systematic review and meta-analysis. ACE, adverse childhood experience; MM, multimorbidity; DRMA, dose–response meta-analysis

All studies were observational in design, and so risk of bias assessments were performed using the ROBINS-E tool (Additional File 1: Table S3) [ 34 ]. There were some consistent risks observed across the studies, especially in domain 1 (risk of bias due to confounding) and domain 3 (risk of bias due to participant selection). In domain 1, most studies were ‘high risk’ ( n  = 24) as they controlled for variables that could have been affected by ACE exposure (e.g. smoking status) [ 40 , 41 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 ]. In domain 3, some studies were ‘high risk’ ( n  = 7) as participant selection was based on participant characteristics that could have been influenced by ACE exposure (e.g. through recruitment at an outpatient clinic) [ 45 , 48 , 49 , 51 , 53 , 54 , 58 ]. The remaining studies were deemed as having ‘some concerns’ ( n  = 18) as participant selection occurred at a time after ACE exposure, introducing a risk of survivorship bias [ 40 , 41 , 42 , 43 , 44 , 46 , 47 , 50 , 52 , 55 , 56 , 57 , 59 , 60 , 61 , 62 , 63 , 64 ].

Key differences in risk of bias were seen in domain 2 (risk of bias due to exposure measurement) and domain 5 (risk of bias due to missing data). In domain 2, some studies were ‘high risk’ as they used a narrow or atypical measure of ACEs ( n  = 8) [ 40 , 42 , 44 , 46 , 55 , 56 , 60 , 64 ]; others were graded as having ‘some concerns’ as they used a broader but still incomplete measure of ACEs ( n  = 8) [ 43 , 45 , 48 , 49 , 50 , 52 , 54 , 62 ]; the remainder were ‘low risk’ as they used an established or comprehensive list of ACE questions [ 41 , 47 , 51 , 53 , 57 , 58 , 59 , 61 , 63 ]. In domain 5, some studies were ‘high risk’ as they failed to acknowledge or appropriately address missing data ( n  = 7) [ 40 , 42 , 43 , 45 , 51 , 53 , 60 ]; others were graded as having ‘some concerns’ as they had a significant amount of missing data (> 10% for exposure, outcome, or confounders) but mitigated for this with appropriate strategies ( n  = 6) [ 41 , 50 , 56 , 57 , 62 , 64 ]; the remainder were ‘low risk’ as they reported low levels of missing data ( n  = 12) [ 44 , 46 , 47 , 48 , 49 , 52 , 54 , 55 , 58 , 59 , 61 , 63 ].

Most studies assessed an exposure that was ‘adverse childhood experiences’ ( n  = 10) [ 41 , 42 , 50 , 51 , 53 , 57 , 58 , 61 , 63 , 64 ], ‘childhood maltreatment’ ( n  = 6) [ 44 , 45 , 46 , 48 , 49 , 59 ], or ‘childhood adversity’ ( n  = 3) [ 47 , 54 , 62 ]. The other exposures studied were ‘birth phase relative to World War Two’ [ 40 ], ‘childhood abuse’ [ 43 ], ‘childhood disadvantage’ [ 56 ], ‘childhood racial discrimination’ [ 55 ], ‘childhood trauma’ [ 52 ], and ‘quality of childhood’ (all n  = 1) [ 60 ]. More than half of studies ( n  = 13) did not provide a formal definition of their exposure of choice [ 42 , 43 , 44 , 45 , 49 , 52 , 53 , 54 , 57 , 58 , 60 , 61 , 64 ]. The upper age limit for childhood ranged from < 15 to < 18 years with the most common cut-off being < 18 years ( n  = 9). The median number of ACEs measured in each study was 7 (IQR 4–10). In total, 58 different ACEs were reported; 17 ACEs were reported by at least three studies, whilst 33 ACEs were reported by only one study. The most frequently reported ACEs were physical abuse ( n  = 19) and sexual abuse ( n  = 16) (Table  1 ). The exposure details for each study can be found in Additional File 1: Table S4.

Thirteen studies provided sufficient data to allow for a meta-analysis of the prevalence of exposure to ≥ 1 ACE; the pooled prevalence was 48.1% (95% CI 33.4 to 63.1%, I 2  = 99.9%, Cochran Q  = 18,092, p  < 0.001) (Fig.  2 ) [ 41 , 43 , 44 , 46 , 47 , 49 , 50 , 52 , 53 , 57 , 59 , 61 , 63 ]. Six studies provided sufficient data to allow for a meta-analysis of the prevalence of exposure to ≥ 4 ACEs; the pooled prevalence was 12.3% (95% CI 3.5 to 35.4%, I 2  = 99.9%, Cochran Q  = 9071, p  < 0.001) (Additional File 1: Fig. S1) [ 46 , 50 , 51 , 53 , 59 , 63 ].

Meta-analysis of prevalence of exposure to ≥ 1 adverse childhood experiences. Meta-analysis of prevalence of exposure to ≥ 1 adverse childhood experience. ACE, adverse childhood experience; CI, confidence interval

Thirteen studies explicitly assessed multimorbidity as an outcome, and all of these defined the threshold for multimorbidity as the presence of two or more LTCs [ 40 , 41 , 42 , 44 , 46 , 47 , 50 , 55 , 57 , 60 , 61 , 62 , 64 ]. The remaining studies assessed comorbidities, morbidity, or disease counts [ 43 , 45 , 48 , 49 , 51 , 52 , 53 , 54 , 56 , 58 , 59 , 63 ]. The median number of LTCs measured in each study was 14 (IQR 12–21). In total, 115 different LTCs were reported; 36 LTCs were reported by at least three studies, whilst 63 LTCs were reported by only one study. Two studies did not report the specific LTCs that they measured [ 51 , 53 ]. The most frequently reported LTCs were hypertension ( n  = 22) and diabetes ( n  = 19) (Table  2 ). Fourteen studies included at least one mental health LTC. The outcome details for each study can be found in Additional File 1: Table S5.

Fifteen studies provided sufficient data to allow for a meta-analysis of the prevalence of multimorbidity; the pooled prevalence was 34.5% (95% CI 23.4 to 47.5%, I 2  = 99.9%, Cochran Q  = 24,072, p  < 0.001) (Fig.  3 ) [ 40 , 41 , 44 , 46 , 47 , 49 , 50 , 51 , 52 , 55 , 57 , 58 , 59 , 60 , 63 ].

Meta-analysis of prevalence of multimorbidity. Meta-analysis of prevalence of multimorbidity. CI, confidence interval; LTC, long-term condition; MM, multimorbidity

All studies reported significant positive associations between measures of ACE and multimorbidity, though they varied in their means of analysis and reporting of the relationship. Nine studies reported an association between the number of ACEs (variably considered as a continuous or categorical parameter) and multimorbidity [ 41 , 43 , 46 , 47 , 50 , 56 , 57 , 61 , 64 ]. Eight studies reported an association between the number of ACEs and comorbidity counts in specific patient populations [ 45 , 48 , 49 , 51 , 53 , 58 , 59 , 63 ]. Six studies reported an association between individual ACEs or ACE subgroups and multimorbidity [ 42 , 43 , 44 , 47 , 55 , 62 ]. Two studies incorporated a measure of frequency within their ACE measurement tool and reported an association between this ACE score and multimorbidity [ 52 , 54 ]. Two studies reported an association between proxy measures for ACEs and multimorbidity; one reported ‘birth phase relative to World War Two’, and the other reported a self-report on the overall quality of childhood [ 40 , 60 ].

Eight studies, involving a total of 197,981 participants, provided sufficient data (either in the primary text, or following author correspondence) for quantitative synthesis [ 41 , 46 , 47 , 49 , 50 , 51 , 57 , 58 ]. Log-linear (Fig.  4 ) and non-linear (Additional File 1: Fig. S2) random effects models were compared for goodness of fit: the Wald-type test for linearity was non-significant ( χ 2  = 3.7, p  = 0.16) and the AIC was lower for the linear model (− 7.82 vs 15.86) indicating that the log-linear assumption was valid. There was a significant dose-dependent relationship between ACE exposure and multimorbidity ( p  < 0.001), with every additional ACE exposure contributing to a 12.9% (95% CI 7.9 to 17.9%) increase in the odds for multimorbidity ( I 2  = 76.9%, Cochran Q  = 102, p  < 0.001).

Dose–response meta-analysis of the relationship between adverse childhood experiences and multimorbidity. Dose–response meta-analysis of the relationship between adverse childhood experiences and multimorbidity. Solid black line represents the estimated relationship; dotted black lines represent the 95% confidence intervals for this estimate. ACE, adverse childhood experience

This systematic review and meta-analysis synthesised the literature on ACEs and multimorbidity and showed a dose-dependent relationship across a large number of participants. Each additional ACE exposure contributed to a 12.9% (95% CI 7.9 to 17.9%) increase in the odds for multimorbidity. This adds to previous meta-analyses that have shown an association between ACEs and individual LTCs, health behaviours, and other health outcomes [ 1 , 28 , 31 , 65 , 66 ]. However, we also identified substantial inter-study heterogeneity that is likely to have arisen due to variation in the definitions, methodology, and analysis of the included studies, and so our results should be interpreted with these limitations in mind.

Although 25 years have passed since the landmark Adverse Childhood Experiences Study by Felitti et al. [ 3 ], there is still no consistent approach to determining what constitutes an ACE. This is reflected in this review, where fewer than half of the 58 different ACEs ( n  = 25, 43.1%) were reported by more than one study and no study reported more than 15 ACEs. Even ACE types that are commonly included are not always assessed in the same way [ 67 ], and furthermore, the same question can be interpreted differently in different contexts (e.g. physical punishment for bad behaviour was socially acceptable 50 years ago but is now considered physical abuse in the UK). Although a few validated questionnaires exist, they often focus on a narrow range of ACEs; for example, the childhood trauma questionnaire demonstrates good reliability and validity but focuses on interpersonal ACEs, missing out on household factors (e.g. parental separation), and community factors (e.g. bullying) [ 68 ]. Many studies were performed on pre-existing research cohorts or historic healthcare data, where the study authors had limited or no influence on the data collected. As a result, very few individual studies reported on the full breadth of potential ACEs.

ACE research is often based on ACE counts, where the types of ACEs experienced are summed into a single score that is taken as a proxy measure of the burden of childhood stress. The original Adverse Childhood Experiences Study by Felitti et al. took this approach [ 3 ], as did 17 of the studies included in this review and our own quantitative synthesis. At the population level, there are benefits to this: ACE counts provide quantifiable and comparable metrics, they are easy to collect and analyse, and in many datasets, they are the only means by which an assessment of childhood stress can be derived. However, there are clear limitations to this method when considering experiences at the individual level, not least the inherent assumptions that different ACEs in the same person are of equal weight or that the same ACE in different people carries the same burden of childhood stress. This limitation was strongly reinforced by our patient and public involvement group (CPAG). Two studies in this review incorporated frequency within their ACE scoring system [ 52 , 54 ], which adds another dimension to the assessment, but this is insufficient to understand and quantify the ‘impact’ of an ACE within an epidemiological framework.

The definitions of multimorbidity were consistent across the relevant studies but the contributory long-term conditions varied. Fewer than half of the 115 different LTCs ( n  = 52, 45.2%) were reported by more than one study. Part of the challenge is the classification of healthcare conditions. For example, myocardial infarction is commonly caused by coronary heart disease, and both are a form of heart disease. All three were reported as LTCs in the included studies, but which level of pathology should be reported? Mental health LTCs were under-represented within the condition list, with just over half of the included studies assessing at least one ( n  = 14, 56.0%). Given the strong links between ACEs and mental health, and the impact of mental health on quality of life, this is an area for improvement in future research [ 31 , 32 ]. A recent Delphi consensus study by Ho et al. may help to address these issues: following input from professionals and members of the public they identified 24 LTCs to ‘always include’ and 35 LTCs to ‘usually include’ in multimorbidity research, including nine mental health conditions [ 9 ].

As outlined in the introduction, there is a strong evidence base supporting the link between ACEs and long-term health outcomes, including specific LTCs. It is not unreasonable to extrapolate this association to ACEs and multimorbidity, though to our knowledge, the pathophysiological processes that link the two have not been precisely identified. However, similar lines of research are being independently followed in both fields and these areas of overlap may suggest possible mechanisms for a relationship. For example, both ACEs and multimorbidity have been associated with markers of accelerated epigenetic ageing [ 69 , 70 ], mitochondrial dysfunction [ 71 , 72 ], and inflammation [ 22 , 73 ]. More work is required to better understand how these concepts might be linked.

This review used data from a large participant base, with information from 372,162 people contributing to the systematic review and information from 197,981 people contributing to the dose–response meta-analysis. Data from the included studies originated from a range of sources, including healthcare settings and dedicated research cohorts. We believe this is of a sufficient scale and variety to demonstrate the nature and magnitude of the association between ACEs and multimorbidity in these populations.

However, there are some limitations. Firstly, although data came from 11 different countries, only two of those were from outside Europe and North America, and all were from either high- or middle-income countries. Data on ACEs from low-income countries have indicated a higher prevalence of any ACE exposure (consistently > 70%) [ 74 , 75 ], though how well this predicts health outcomes in these populations is unknown.

Secondly, studies in this review utilised retrospective participant-reported ACE data and so are at risk of recall and reporting bias. Studies utilising prospective assessments are rare and much of the wider ACE literature is open to a similar risk of bias. To date, two studies have compared prospective and retrospective ACE measurements, demonstrating inconsistent results [ 76 , 77 ]. However, these studies were performed in New Zealand and South Africa, two countries not represented by studies in our review, and had relatively small sample sizes (1037 and 1595 respectively). It is unclear whether these are generalisable to other population groups.

Thirdly, previous research has indicated a close relationship between ACEs and childhood socio-economic status (SES) [ 78 ] and between SES and multimorbidity [ 10 , 79 ]. However, the limitations of the included studies meant we were unable to separate the effect of ACEs from the effect of childhood SES on multimorbidity in this review. Whilst two studies included childhood SES as covariates in their models, others used measures from adulthood (such as adulthood SES, income level, and education level) that are potentially influenced by ACEs and therefore increase the risk of bias due to confounding (Additional File 1: Table S3). Furthermore, as for ACEs and multimorbidity, there is no consistently applied definition of SES and different measures of SES may produce different apparent effects [ 80 ]. The complex relationships between ACEs, childhood SES, and multimorbidity remain a challenge for research in this field.

Fourthly, there was a high degree of heterogeneity within included studies, especially relating to the definition and measurement of ACEs and multimorbidity. Whilst this suggests that our results should be interpreted with caution, it is reassuring to see that our meta-analysis of prevalence estimates for exposure to any ACE (48.1%) and multimorbidity (34.5%) are in line with previous estimates in similar populations [ 2 , 11 ]. Furthermore, we believe that the quantitative synthesis of these relatively heterogenous studies provides important benefit by demonstrating a strong dose–response relationship across a range of contexts.

Our results strengthen the evidence supporting the lasting influence of childhood conditions on adult health and wellbeing. How this understanding is best incorporated into routine practice is still not clear. Currently, the lack of consistency in assessing ACEs limits our ability to understand their impact at both the individual and population level and poses challenges for those looking to incorporate a formalised assessment. Whilst most risk factors for disease (e.g. blood pressure) are usually only relevant within healthcare settings, ACEs are relevant to many other sectors (e.g. social care, education, policing) [ 81 , 82 , 83 , 84 ], and so consistency of assessment across society is both more important and more challenging to achieve.

Some have suggested that the evidence for the impact of ACEs is strong enough to warrant screening, which would allow early identification of potential harms to children and interventions to prevent them. This approach has been implemented in California, USA [ 85 , 86 , 87 ]. However, this is controversial, and others argue that screening is premature with the current evidence base [ 88 , 89 , 90 ]. Firstly, not everyone who is exposed to ACEs develops poor health outcomes, and it is not clear how to identify those who are at highest risk. Many people appear to be vulnerable, with more adverse health outcomes following ACE exposure than those who are not exposed, whilst others appear to be more resilient, with good health in later life despite multiple ACE exposures [ 91 ] It may be that supportive environments can mitigate the long-term effects of ACE exposure and promote resilience [ 92 , 93 ]. Secondly, there are no accepted interventions for managing the impact of an identified ACE. As identified above, different ACEs may require input from different sectors (e.g. healthcare, social care, education, police), and so collating this evidence may be challenging. At present, ACEs screening does not meet the Wilson-Jungner criteria for a screening programme [ 94 ].

Existing healthcare systems are poorly designed to deal with the complexities of addressing ACEs and multimorbidity. Possibly, ways to improve this might be allocating more time per patient, prioritising continuity of care to foster long-term relationships, and greater integration between different healthcare providers (most notably primary vs secondary care teams, or physical vs mental health teams). However, such changes often demand additional resources (e.g. staff, infrastructure, processes), which are challenging to source when existing healthcare systems are already stretched [ 95 , 96 ]. Nevertheless, increasing the spotlight on ACEs and multimorbidity may help to focus attention and ultimately bring improvements to patient care and experience.

ACEs are associated with a range of poor long-term health outcomes, including harmful health behaviours and individual long-term conditions. Multimorbidity is becoming more common as global populations age, and it increases the complexity and cost of healthcare provision. This is the first systematic review and meta-analysis to synthesise the literature on ACEs and multimorbidity, showing a statistically significant dose-dependent relationship across a large number of participants, albeit with a high degree of inter-study heterogeneity. This consolidates and enhances an increasing body of data supporting the role of ACEs in determining long-term health outcomes. Whilst these observational studies do not confirm causality, the weight and consistency of evidence is such that we can be confident in the link. The challenge for healthcare practitioners, managers, policymakers, and governments is incorporating this body of evidence into routine practice to improve the health and wellbeing of our societies.

Availability of data and materials

No additional data was generated for this review. The data used were found in the referenced papers or provided through correspondence with the study authors.

Abbreviations

Adverse childhood experience

Akaike information criterion

CONSORTIUM Against pain inequality

Confidence interval

Chronic pain advisory group

Interquartile range

Long-term condition

International prospective register of systematic reviews

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Acknowledgements

The authors thank the members of the CAPE CPAG patient and public involvement group for providing insights gained from relevant lived experiences.

The authors are members of the Advanced Pain Discovery Platform (APDP) supported by UK Research & Innovation (UKRI), Versus Arthritis, and Eli Lilly. DS is a fellow on the Multimorbidity Doctoral Training Programme for Health Professionals, which is supported by the Wellcome Trust [223499/Z/21/Z]. BT, BS, and LC are supported by an APDP grant as part of the Partnership for Assessment and Investigation of Neuropathic Pain: Studies Tracking Outcomes, Risks and Mechanisms (PAINSTORM) consortium [MR/W002388/1]. TH and LC are supported by an APDP grant as part of the Consortium Against Pain Inequality [MR/W002566/1]. The funding bodies had no role in study design, data collection/analysis/interpretation, report writing, or the decision to submit the manuscript for publication.

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DS and LC contributed to review conception and design. DC, BT, BS, TH, LM, and LC contributed to search strategy design. DS and BT contributed to study selection and data extraction, with input from LC. DS and BT accessed and verified the underlying data. DS conducted the meta-analyses, with input from BT, BS, TH, LM, and LC. DS drafted the manuscript, with input from DC, BT, BS, TH, LM, and LC. DC, BT, BS, TH, LM, and LC read and approved the final manuscript.

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12916_2024_3505_moesm1_esm.docx.

Additional File 1: Tables S1-S5 and Figures S1-S2. Table S1: Search strategy, Table S2: Characteristics of studies included in the systematic review, Table S3: Risk of bias assessment (ROBINS-E), Table S4: Exposure details (adverse childhood experiences), Table S5: Outcome details (multimorbidity), Figure S1: Meta-analysis of prevalence of exposure to ≥4 adverse childhood experiences, Figure S2: Dose-response meta-analysis of the relationship between adverse childhood experiences and multimorbidity (using a non-linear/restricted cubic spline model).

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Senaratne, D.N.S., Thakkar, B., Smith, B.H. et al. The impact of adverse childhood experiences on multimorbidity: a systematic review and meta-analysis. BMC Med 22 , 315 (2024). https://doi.org/10.1186/s12916-024-03505-w

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Application of artificial intelligence in dental crown prosthesis: a scoping review

• Hyun-Jun Kong 1 &
• Yu-Lee Kim 2  

BMC Oral Health volume  24 , Article number:  937 ( 2024 ) Cite this article

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In recent years, artificial intelligence (AI) has made remarkable advancements and achieved significant accomplishments across the entire field of dentistry. Notably, efforts to apply AI in prosthodontics are continually progressing. This scoping review aims to present the applications and performance of AI in dental crown prostheses and related topics.

We conducted a literature search of PubMed, Scopus, Web of Science, Google Scholar, and IEEE Xplore databases from January 2010 to January 2024. The included articles addressed the application of AI in various aspects of dental crown treatment, including fabrication, assessment, and prognosis.

The initial electronic literature search yielded 393 records, which were reduced to 315 after eliminating duplicate references. The application of inclusion criteria led to analysis of 12 eligible publications in the qualitative review. The AI-based applications included in this review were related to detection of dental crown finish line, evaluation of AI-based color matching, evaluation of crown preparation, evaluation of dental crown designed by AI, identification of a dental crown in an intraoral photo, and prediction of debonding probability.

Conclusions

AI has the potential to increase efficiency in processes such as fabricating and evaluating dental crowns, with a high level of accuracy reported in most of the analyzed studies. However, a significant number of studies focused on designing crowns using AI-based software, and these studies had a small number of patients and did not always present their algorithms. Standardized protocols for reporting and evaluating AI studies are needed to increase the evidence and effectiveness.

Peer Review reports

Artificial intelligence (AI) refers to the capability of computers to perform tasks that normally require human intelligence, such as learning, reasoning, and problem-solving. In medicine, AI is used to identify and categorize pathologies in radiographs and photographs, predict clinical events, and simulate drug interactions with targets [ 1 , 2 , 3 ] Similar to its transformative impact in medicine, AI research has surged in dentistry, demonstrating its potential in a variety of areas including diagnosis, prevention, and treatment [ 4 , 5 , 6 ]. In dentistry, AI is applied in several diagnostic tasks: identifying dental caries from radiographs [ 7 , 8 ], assessing the complexity of endodontic cases [ 9 , 10 ], automating cephalometric landmark localization [ 11 ], and classifying dental implant systems [ 12 , 13 , 14 ]. The majority of AI applications is based on machine learning, a methodology where mathematical models are trained to recognize statistical patterns within datasets to perform predictions. A subset of machine learning known as deep learning employs multi-layered neural networks with intricate architecture, allowing deep learning algorithms that often surpass other machine learning strategies in discerning patterns within vast and varied datasets [ 15 ]. This is particularly advantageous in the field of dentistry, where datasets often encompass images, proteomic information, and clinical data [ 16 ].

Prosthodontics stands at the intersection of artistic expression and scientific principles within the field of dentistry [ 17 ]. It constitutes the art and science involved in the diagnosis, strategic planning, rehabilitation, and preservation of the functional, comfortable, aesthetically pleasing, and healthy aspects of the oral structures in patients. Its primary objective is the replacement of absent teeth and related structures through the integration of artificial substitutes. The application of AI holds considerable promise across various therapeutic modalities within this domain [ 18 ].

The implementation of AI is significantly impacting the creation of dental crown prostheses, a fundamental component of prosthodontic dentistry. The dental crown prosthesis plays an integral role in reinstating both the structural integrity and functionality of teeth affected by damage or decay, offering patients solutions that are both visually appealing and durable. The integration of AI in this field holds the potential to transform the processes involved in designing, manufacturing, and placing dental crowns.

Despite increasing publications on deep learning in dental crown prostheses, there is uncertainty about the prevalent tasks, preferred methods, and performance variations. This scoping review aims to evaluate studies on deep learning applications in dental crown prostheses, addressing these uncertainties

The workflow of this study is shown in Fig. 1 . We followed the reporting recommendations specified in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews (PRISMA-ScR) guidelines [ 19 ] to convey the findings of this investigation. The specific review question was the applications and performance of AI in dental crown prostheses.

The workflow of the study consists of three steps: database search, screening, and literature review

Our literature exploration was based on the PICO (problem/patient/population, intervention/indicator, comparison, and outcome) elements [ 20 ].

Population: Images and other data types for dental crown prostheses used in prosthodontic rehabilitation.

Intervention/Comparison: AI models for diagnosis, prognosis assessment, and treatment procedures compared to reference standards.

Outcome: Any type of performance measurement.

Literature search

An electronic literature search was conducted in January 2024 across five databases: PubMed, Scopus, Web of Science, Google Scholar, and IEEE Xplore. We focused on literature published after 2010 to capture the most relevant and recent advancements in deep learning applications in dentistry. Manual searches and searches for gray literature were not conducted.

Search terms were developed and combined by two reviewers (H.J.K. and Y.L.K.) with reference to previous studies [ 16 , 18 ]. Each category consists of a combination of Medical Subject Headings (MeSH) Terms and related dental terms with conjunctions: (“dental crown” OR “crown preparation” OR “fixed prosthesis” OR “prosthodontic” OR “dental prosthesis”) and (“artificial intelligence” OR “machine learning” OR “deep learning” OR “neural network”).

Eligibility criteria

The following inclusion criteria were employed in the selection of articles:

Articles related to AI applications in dental crown prosthesis

Articles composed in English and released between January 2010 and January 2024

Our exclusion criteria were:

Articles that used AI for conditions not related to dental crown prosthesis

Articles that did not report performance metrics such as accuracy

Articles without the full text available

Review articles and letters to the editor

Two reviewers (H.J.K. and Y.L.K.) assessed the titles and abstracts of articles based on pre-established inclusion and exclusion criteria. When titles and abstracts were deemed insufficient in providing necessary information, a thorough analysis of the entire text was conducted. Both reviewers diligently examined articles that were potentially relevant and collaboratively selected papers for further analysis. Any discrepancies in opinions were resolved through discussion.

Selection of sources

The flowchart in Fig. 2 outlines the article selection process adhering to PRISMA-ScR for this scoping review. Initially, a search of electronic literature produced 393 records, which was decreased to 315 after eliminating duplicate references. Following the examination of titles and abstracts, 26 studies underwent a more detailed review, after which 14 records were excluded for not meeting the inclusion criteria. Finally, 12 eligible publications were included in the qualitative review (Table 1 ). The evaluators unanimously agreed on the literature selection and categorization of publications.

PRISMA-ScR flowchart of study selection

Characteristics of the included studies

The AI-based applications included in this review were related to detection of dental crown finish line, evaluation of AI-based color matching, evaluation of crown preparation, evaluation of dental crown designed by AI, identification of dental crowns in intraoral photos, and prediction of debonding probability (Fig. 3 ). While the search was initially planned to encompass articles published between January 2010 and January 2024, the findings indicate a surge in the popularity of AI applications starting in 2019.

Number of included articles by publication year and purpose of artificial intelligence application

The dataset size exhibited a wide range owing to the diversity in inputs and outcomes across study types (Table 2 ). Dataset size for included studies ranged from 12 to 8640. Studies using AI software included a small number of data (mean = 24.25). Since these studies do not learn new models, they do not require large datasets like existing deep learning studies. The most common types of data used were scanned digital images of the jaw and casts ( n =10), and two studies used intraoral photographs.

AI architecture

Three types of AI architecture were used in this body of literature. AI software was used most often (5 times). CNN was used four times, and GAN was used three times. Among AI software, CNN and GAN algorithms were used in two studies. However, in the remaining three documents, the name of the software was provided, although the specific algorithm was not disclosed.

Excluding studies where the algorithm could not be confirmed, in designs using AI, the program used only 3D-GAN or used it in combination with CNN. In other types of studies, CNNs, which are widely used in image classification and object detection, were used. In two studies using a combination of CNN and GAN, CNN was used to extract the preparation tooth and set the margin line, and then GAN was used to create the outer surface.

Outcome metrics

With a scoping review, there is considerable heterogeneity in data forms and methodologies, leading to diverse outcome metrics. In studies evaluating AI design, RMS was used as an evaluation indicator in six of the studies. In these studies, mean deviation to evaluate positional accuracy and cusp angle to evaluate crown shape were used as evaluation indicators. Working time was also included in two studies to compare with existing programs or traditional methods. When an object detection algorithm was used, Intersection over union (IoU) was used as an evaluation index. Accuracy, precision, recall, and F-score were used in one prediction study.

According to this scoping review, an increasing number of studies have employed AI for various tasks related to dental crown prostheses. To align with the rapid evolution of digital technologies, the investigation focused on the most recent 14 years. The application of AI in the fabrication and evaluation of dental crowns can contribute to increased efficiency for prosthodontists, raising expectations for improved productivity. The application of AI to the following fields related to dental crown prosthesis was reviewed.

Dental crown prosthesis designed by AI

The production of crown prostheses has been separated into traditional wax-up methods and digital approaches using CAD/CAM systems. Recently, there has been a widespread adoption of CAD/CAM methodologies, particularly in conjunction with the popularization of zirconia usage. Notably, these methods report high levels of accuracy and success rates [ 33 ]. In the CAD/CAM process, there have been efforts to enhance the speed and precision of prosthesis design through the application of AI [ 34 ].

Seven studies evaluated the feasibility of AI models to design dental crown prostheses [21,22,25,28,29,31,32. Four studies used AI software [ 25 , 28 , 31 , 32 ], while three studies [ 21 , 22 , 29 ] employed 3D-GAN algorithms for model training. In six studies, integration of AI into the fabrication process demonstrated higher accuracy compared with traditional CAD or manually designed methods. One study [ 28 ] reported that knowledge-based AI, compared to human-designed CAD software, exhibited a higher occlusal profile discrepancy.

Two studies [ 25 , 31 ] reported high time efficiency of AI-based programs. While traditional CAD work does not involve adding and modifying wax, it requires human thinking. Both wax-up and CAD processes are heavily influenced by the accumulated experience of dental technicians [ 35 , 36 ]. However, AI-based operations minimize human intervention using automated calculations. Therefore, designing with AI significantly reduces the time spent on the design process, especially in cases with extensive restoration requirements.

Among the seven studies, four used commercially produced AI software, with two of them lacking specific mention of the program's algorithm [ 25 , 28 ]. The absence of detailed information on the algorithms and metrics used for training the models in these studies acts as a limitation, emphasizing the need for transparency in the application of AI in dentistry, especially with commercially available software. Additionally, studies employing software had datasets ranging from 12 to 30 cases, posing a limitation in detecting statistical significance due to the potentially insufficient sample size. Despite these limitations, AI for dental crown design has the potential to significantly increase production efficiency by saving time. Considering the performance demonstrated in aspects such as morphology, internal fit, and occlusion, there is a promising outlook for the future utilization of AI in dentistry.

Detection of dental crown finish line

Choi et al. [ 23 ] compared the accuracy of hybrid software combined with deep learning with existing traditional CAD software in detecting the crown finish line. An accurate marginal fit is crucial for preventing microgaps. This, in turn, lowers the risk of caries and ensures that the restoration retains its function [ 37 ]. Recently, finish lines have been extracted and processed manually using CAD programs, but this is a repetitive and time-consuming process [ 38 ]. In Choi et al., as a result of evaluation using Hausdorff distance and chamfer distance, the hybrid system showed statistically more accurate results. This implies that a hybrid approach, integrating both deep learning and computer-aided design methods, may allow robust and precise extraction of finish lines with minimal adjustments required.

Evaluation of crown preparation

One of the most fundamental aspects in dental prosthodontics education is understanding and practicing the principles of tooth preparation [ 39 ]. However, evaluating students' tooth preparation outcomes in dental education can lack consistency due to factors such as subjective grading scales and insufficient inter-rater agreement. This difficulty hinders the provision of ongoing and reliable feedback [ 40 , 41 ].

Han et al. [ 27 ] assessed the viability of software-based automated evaluation (SAE) with AI to evaluate abutment tooth preparation for single crowns. This was done through a comparison with a human-based digitally-assisted evaluation (DAE), which showed perfect intra-rater agreement and almost perfect inter-rater agreement with SAE. The findings of this study substantiate the credibility of SAE within prosthodontics education and propose its potential clinical utility for evaluating tooth preparation

Evaluation of AI-based color matching

A crucial aspect of the dental technician's role is replicating the natural color of teeth in dental prostheses. An experienced dental technician possesses the ability to precisely assess the authentic color. However, this proves to be a challenging task for a less-experienced dental technician [ 42 ].

Ueki et al. [ 26 ] extracted 62 images of patient teeth, which were annotated by experienced dental technicians. They then used a neural network to estimate the true color. The accuracy of the first candidate's output was six of 22 (27%), considerably lower than the desired level. However, the outputs for the second and third candidates encompassed 12 (55%) and 15 (68%) of the total 22 images, respectively. This affirmed accurate classification of certain colors.

One notable limitation of this study is the relatively small size of the image dataset used. To more accurately assess the potential of AI in shade selection, a substantial amount of training data is required.

Identification of dental crown in intraoral photo

In clinical situations, it is crucial for dentists to gather intraoral information about patients—a process that demands time and effort. Additionally, the effectiveness of this procedure relies on the dentist's knowledge and experience. Consequently, there is a demand for an automated system that can rapidly assess the intraoral situation.

Takahashi et al. [ 24 ] used a deep learning object detection method to recognize dental prostheses and restorations. In their study, ‘You Only Look Once version 3’ (YOLOv3) was used for object detection because it has shown high performance in other dental deep learning studies [ 43 , 44 , 45 ].

A satisfactory level of performance is typically associated with an IoU exceeding 0.7 [ 46 , 47 ]. In the present investigation, the IoU was 0.76. Consequently, the proficiency of this learning system was high. In assessing the accuracy of the object detection model, the mAP is employed, with values above 0.7 considered favorable in previous research [ 48 ]. The mAP achieved in the present study was 0.80, supporting the learning system's commendable performance from a mAP perspective.

Irrespective of the overall count of objects across all images, there was a tendency for higher average precision (AP) scores in cases of metallic-colored prostheses, while tooth-colored prostheses exhibited a tendency toward lower AP scores. These findings suggest that the identification was influenced by the color distinctions between the natural teeth and prostheses.

Prediction of debonding probability

CAD/CAM composite resin (CR) crowns cemented to dentin often exhibit a propensity for debonding within one year, and the reported debonding rate for CAD/CAM CR crowns cemented on implant abutments stands at 80% within one year [ 49 ]. Inadequate preparation has been identified to contribute to debonding [ 50 , 51 ].

Yamaguchi et al. [ 30 ] aimed to predict the debonding probability of CAD/CAM CR crowns using scanned images of prepared models employing convolutional neural networks. The reported prediction accuracy was 98.5%. Despite the good performance, this study acknowledges a limitation in explaining the primary factor contributing to debonding, stating that it was difficult to pinpoint the main cause.

Limitations

This study has several limitations. First, as a scoping review, it provides an overview of the current application of AI in dental crown prosthetics and assesses the need for further research, but it does not establish the reliability of existing knowledge as a systematic review would. Second, the reviewed literature was classified into six categories, but half of the articles are included in the category of "evaluation of dental crowns designed by AI," with only one article in each of the other categories. Lastly, some of the articles included in the review lack transparency as the algorithms used are not clearly specified.

In addition to the articles reviewed in this study, there are an increasing number of studies integrating next-generation technologies, such as robotics, into dental crown prosthesis [ 52 , 53 ]. The advancement of these technologies, including AI, will bring continuous progress to the entire field of prosthodontics.

The number of studies applying AI to dental crown prostheses is gradually increasing. According to the results of this review, AI has the potential to increase efficiency in processes such as fabricating and evaluating dental crowns, with a high level of accuracy reported in most of the included studies. However, a significant number of studies focused on designing crowns using AI-based software, and these studies have limitations in that the study size was small and the algorithms used were sometimes not disclosed. The small number of AI-related studies means that AI application to dental crowns is needed in more diverse aspects. Additionally, research involving a large number of patients and data in various clinical situations is needed. AI study, by its nature, uses a variety of methods and evaluation metrics. Therefore, standardized protocols for reporting and evaluating AI studies are needed to increase the evidence and effectiveness.

Availability of data and materials

All data generated or analysed during this study are included in this published article.

Abbreviations

• Artificial intelligence

Computer-aided design

Computer-aided design/computer-aided manufacturing

Convolutional neural network

Crown composite resin crown

Digitally-assisted evaluation

Deep convolutional generative adversarial network

Two-stage deep generative adversarial network

Generative adversarial network

Software-based automated evaluation

Intersection over union

Root mean square error

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This study was supported by Wonkwang University in 2024.

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HJK conceived the study. All authors developed the review protocol. HJK and YLK did the literature search and assessed the quality of included studies. All authors read, commented critically and approved the final manuscript.

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Kong, HJ., Kim, YL. Application of artificial intelligence in dental crown prosthesis: a scoping review. BMC Oral Health 24 , 937 (2024). https://doi.org/10.1186/s12903-024-04657-0

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