how old can references be in a research paper

How Old Should Your Article References Be? Based on 3,823,919 Examples

I analyzed 3,823,919 references cited in 96,685 research papers, chosen at random from those uploaded to PubMed Central between the years 2016 and 2021, in order to answer the question:

How to determine if a reference is too old to be included in a research article?

I used the BioC API to download the data (see the References section below).

Here’s a summary of the key findings

1- When searching for references to cite, you should aim to find those published within the past 13 years . However, 25% of references cited in published research papers are older than this, and there is no convincing evidence that higher-quality articles cite more recent sources.

2- Looking at the same data from the author’s point of view , we can say that: You should not expect your paper to get cited a lot within its first year of publication, the estimated peak will be after 3 to 13 years , then it will gradually taper off, but your paper can still get cited even 27 years after publication!

How old is the average cited source?

Looking at the density plot below we see that:

A large portion of references cited in research papers is less than 5-years-old, and the majority is less than 10-years-old.

how old can references be in a research paper

Note that the reference age is calculated by subtracting the publication year of the reference from that of the paper citing it.

The table below shows that:

The median reference cited in a research paper is 7-years-old, and 75% of references were published within the past 13-years. Still, 5% of papers cited sources older than 27 years, some even used historical sources.

Minimum Reference Age	0 years old
5th Percentile	1 year old
25th Percentile	3 years old
50th Percentile (Median)	7 years old
Mean Reference Age	9.78 years old
75th Percentile	13 years old
95th Percentile	27 years old
Maximum Reference Age	2020 years old

Do higher-quality articles cite more recent sources?

In order to answer this question, the quality of a given article will be judged by the impact factor of the journal in which it was published. Although impact factors are not perfect measures of quality, it could be argued that they provide a good proxy for our purposes.

So I collected the journal impact factor (JIF) for 71,579 articles and divided the dataset into 2 groups:

research papers published in low impact journals (JIF ≤ 3): this subset consisted of 34,758 articles and 1,247,373 references
research papers published in high impact journals (JIF > 3): this subset consisted of 36,821 articles and 1,791,061 references

The median reference in both groups was 7-years-old, the mean however was different: the average reference in the first group was 10.1-years-old and in the second group was 9.3-years-old. So there isn’t enough evidence to conclude that higher quality articles reference more recent sources.

Comeau DC, Wei CH, Islamaj Doğan R, and Lu Z. PMC text mining subset in BioC: about 3 million full text articles and growing, Bioinformatics , btz070, 2019.

FAQ: How old should or can a source be for my research?

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Last Updated: Jul 18, 2024 Views: 129929

How old your research sources can be, using the publication date or date of creation as the defining criteria, is either stated in your assignment rubric or depends on your field of study or academic discipline. If it’s a requirement for your assignment, look for words like “sources must be published in the last 10 years” or words to that effect that specify the publication date or range required. If the currency of sources is not a requirement of your assignment, think about the course involved and what an appropriate age might be.

How fast-changing is the field of study?

Sources for a history paper might, by their very nature, be older if they are diaries, personal letters, or other documents created long ago and used as primary sources. Sources used for research in the sciences (health care, nursing, engineering), business and finance, and education and other social science fields require more “cutting edge” research, as these fields change quickly with the acquisition of new knowledge and the need to share it rapidly with practitioners in those fields.

A good rule of thumb is to use sources published in the past 10 years for research in the arts, humanities, literature, history, etc.

For faster-paced fields, sources published in the past 2-3 years is a good benchmark since these sources are more current and reflect the newest discoveries, theories, processes, or best practices.

Use the library’s Multi-Search search results page to limit your sources to those published within a date range you specify. Use the Publication Date custom setting seen on the left side of the search results page:

Screenshot of the publication date area in multisearch

For further assistance with this or other search techniques, contact the Shapiro Library email at [email protected] or use our 24/7 chat service.

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Why you should use older references in your thesis

By Julia Hallas, PhD Candidate

“Never use references that are older than three years” was the advice given by a journal article reviewer I went along to hear recently. Yet a postgraduate supervisor who was sitting next to me whispered, “except for seminal papers”. I have heard a number of conflicting opinions about date ranges and types of references to use in a thesis or journal article. Yet such advice can limit one’s thinking and creative capacity, so I think that it’s worthwhile thinking through a strategy and a rationale for the references you decide to include in your research project. Let’s think about how we might define papers as seminal, and if we should ever use references that are older than three years.

Cite influential theories

Seminal papers are those that explain well-known theoretical frameworks and concepts. Such a theory will have been influential in developing a field of study and will be well cited in the literature. For example, I am drawing on Vygotsky’s (1978) ‘zone of proximal development’ theory in my thesis. Many researchers have studied this significant concept over past decades, and I could cite one of those papers, however it would be as a secondary source. Much better for me to build my academic knowledge and integrity by reading Vygotsky and citing him as the original source.

Cite the latest empirical studies

What kind of date range should we be looking at when searching for empirical studies? Do you know how literature is selected in your discipline? I looked for advice in three useful texts on research. In describing how to undertake a literature search, Creswell (2009) did not mention a date range at all; while Merriam (2008) and Cohen, Manion & Morrison (2011) both suggested that only the most recent work in the area should be included in a literature review. There are so many journals and publications today, it would be very difficult for anyone to read all the research on a subject. Therefore common sense must prevail. A sensible strategy would be to discuss with your supervisors a date range that would provide the most up to date work for your study. However once the date range is determined, there is no need to stick rigidly to this. For example, if you notice an older reference that is often cited often in the articles you are reading, check it out. If you still think it’s worth including, cite it as a primary source.

So there you have it. Older articles have their place in thesis writing, as do the most up-to-date empirical studies. Think about the approach you might take and discuss it with your supervisors. They will be pleased to see that you are thinking about this important element of research: how to deal with older and newer references in your thesis writing.

Cohen, L., Manion, L., & Morrison, K. (2011). Research methods in education (7th ed.). Oxon, UK: Routledge.

Creswell, J. W. (2009). Research design: Qualitative, quantitative, and mixed methods approaches (3rd ed.). California, CA: Sage.

Merriam, S. B. (2009). Qualitative Research: A guide to design and implementation . San Francisco, CA: Jossey-Bass.

About Graduate Research School (Auckland University of Technology)

7 thoughts on “ why you should use older references in your thesis ”.

Well Julia thank you for this post. I am finding that many of my references are old indeed especially when dealing with fundamental philosophical issues as many of today’s dilemmas have been explored before. If one accepts a cyclical construct of time and thus Heraclitus, Parmenides and Plato from over 2000 years ago are as relevant as the Upanishads. Ah, but the more recent works of Leibniz, Hegel, Husserl and Sartre are as relevant as Badiou, Latour and Zizek!

I enjoy reading Julia’s posts – always useful topics. Consideration of the age of references is important, but too much emphasis on the age of the reference can overshadow a more important criterion – relevance to the research question. I usually gather what seems relevant – and then look at the time frame covered. That can indicate some gaps but can also tell a story in itself. I could add two additional things: • Does the issue of age of references vary between disciplines? Are there fast moving disciplines such as IT, where older references may have less relevance? • The history of thought can be interesting and/or important. Maybe some of the older thinking may not make it into your thesis, but could be important in defending why a particular approach has been taken. The development of ideas over time on a topic can be an important finding.

I have a question – at what point do you stop? How close to the submission of your thesis can our literature search be expected to cover?

Imagine a scenario – you are a month or a week from sending your final version to a proof-reader. You and your supervisor are happy with what you think is a final version of your thesis. Another article comes out from a highly respected author of considerable standing in the field. What do you do?

Thank you Ross and Katharine for your comments. Katharine I hope a supervisor answers your question because I would like an answer to that one as well. Cheers, Julia

In your thesis write the last date that your literature review was updated. Don’t re-write your thesis if a new publication comes out after the cut-off date unless the new publication is so fundamentally contrary to what you have written in your thesis that it needs an answer. This is almost never. If it is an important update then as a researcher with an ongoing interest in the field then you will naturally have read the publication and have an opinion on it that can be stated when asked.

Well this depends. Older references can be outdated. Still, older sources may be more relevant than newer ones. I guess it all depends on the topic. Basically, there is no formula .

How recent is recent for good referencing?

how long a reserch paper can be considered a recent research works

Cited articles (i.e., references) in a research paper play a central role in demonstrating the necessity of the research and establishing the validity and significance of the research results.

Therefore, good referencing practices (e.g., citing relevant, critical, and recent research works on the topics) not only increase the quality of the research paper but also facilitate its peer review and availability to the right audience.

Citing or referencing recent articles in the research paper assures reviewers that an extensive literature review was undertaken while writing the paper and information in the paper is up to date. This builds trust between the authors of the paper and the reviewers, which may influence peer review reports.

How old is gold?

All being said, do we exactly know how old a research article can be before it gets the label of not being recent i.e., an old article not good for citing.

There is consensus among scientists and researchers that articles less than five years old are recent publications. However, it may vary from discipline to discipline. For example, researchers in fast-moving fields (e.g., nanotechnology or artificial intelligence) may feel 5-years is too old whereas those in biology may not have the same feeling.

How many recent references make a research paper contemporaneous?

Santini et al. (20018) suggested that if the most recent reference is more than 5 years or so, it can indicate that a full up to date review of the literature has not been undertaken.

However, the suggestion is a weak indicator of the comprehensiveness of the literature review done while writing a paper as it is based on the measure of only one reference.

To build a robust understanding of the matter, nXr team analyzed how old references of 69 research papers (published in three highly acclaimed journals: Nature, Science, and Cell) were.

The graph clearly shows that 50% of references in the articles published in highly acclaimed journals are less than 6 years old. This indicates that well-written articles have the characteristic to cite more recent research papers.

How to get similar information for the references in the research paper you are writing?

No worries! When you cite using nXr reference manager and citation tool , nXr automatically creates a dashboard (accessible from your nXr.iLibrary) for the references in your research paper containing various data visualizations.

In one such visualization, you can see the publication year distribution of the references (see below). nXr also gives you an alert if 50% of the references are more than 5 years old so that you can check them.

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How Old Should References be: Best Age of Sources in writing

The Best Age for Your Research References

When you are referencing, it is vital to consider the age of references. It has to be up to date to make your research authentic. Due to the advancement of science, it can be awkward to reference the older content that lost value after being overtaken by the latest scientific steps. Our piece tries to justify this aspect.

How Old Should References be

Before you cite other people’s work, you must think of what can be an appropriate source to support the argument that you are elaborating on.

The best practice is that a reference should not be older than 5 years to ensure that the source is as recent as possible. However, when researching old topics like history and scientific data, your sources can be older since such content requires accuracy over recency.

Regardless, the majority of sources should be within 5 years.

In general, the limit can be ten years but it is good to use the original source before you use the most recent reference.

Any reference that dates 20 to 30 years may be outdated or no longer relevant. Our caution is; you can still include older references where they are applicable.

However, make a proper judgment based on your field of study. You need to place your work in the current content.

People Also Read: What is a Background in an Essay: Introducing Information

Best Places to Get Recent and Credible Sources

1. authority websites.

Several online sources do not have factual information to help you to accomplish your research mission. You have to countercheck the information to establish if it is an authority website or not.

The most reliable websites are the government or other educational websites. Some of the credible websites to use in your research work areas are listed below:

US Census Bureau
UK statistics
The World Factbook
Science.gov

2. Credible Journals

One can determine how credible a journal can be by checking how many times people cited it.

Still, you can find the right information from reviews of other scholars.

You can perform a CRAAP test which involves gauging it through Currency, Relevance, Authority, Accuracy, and Purpose.

You rather take long than cite unreliable materials. Examples of credible journals are:

Oxford Academic
Google Scholar
SAGE Publishing
Microsoft Academic

3. Credible News Sources

One should take more caution while citing news sources because it is difficult to determine unbiased and unreliable ones. You can apply the CRRAP test principle.

In our paper writing guide , we explained that the references should be from credible sources. Now, the most credible ones in this category are listed below:

The Washington Post
The New York Times

People Also Read: Research Paper Due Tomorrow: Not started, we Write in hours

Best Age for Research References

While researching for your essay assignment, it can be fulfilling if you cite your content using credible websites and journals. For example, if you are handling a science-based assignment, you can use references from natural sciences sources like NASA, PopularScience, National Geographic, or Scientific American.

Even better, you can use government entities to advance your research and make your work. One perfect example is the United States Justice Statistics or CIA World Factbook.

Research Papers

When you are writing your research paper, you have varying options to reference your sources. Firstly, you can begin with using credible research journals such as Google Scholar because it is easy to search it on the web.

Thankfully, this Google Scholar is free. Other credible journals in that order are JSTOR, ScienceDirect, Academia, and Scopus.

Besides, you can still use research think tanks which can add value to your efforts. The most common ones are Pew Research Center, Rand Corporation, and the Milken Institute.

Thesis and Dissertations

For you to make your thesis or dissertation content to be credible, you have to reference your work using reliable sources. The most outstanding one is to use information from credible journals like Academia or SAGE Publishing.

Even better, you can cite your work using credible news sources since the institutions still find such sources to be subjective. The most popular ones are BBC News, Google News, CNN, or The Wall Street Journal.

As if that is not enough, you can use academic libraries and databases. Some of the trusted sources within this category are Scopus, ProQuest, and JSTOR.

Factors Determining the Age of References/Sources

1. date of publication.

The date of publication of any research article tells us the age of the sources.

If a website journal indicates the date when they published the article, it becomes a perfect measure of the article’s age.

For example, if you want to cite those articles that are within the ten-year limit, you begin by checking when the websites published the piece.

2. Scientific Developments

Due to scientific advancements, you can encounter the materials in some authority websites which still use outdated concepts.

Since you want to update your piece with the most recent information that indicates basic scientific developments, you can avoid such sources. You can determine the age of that article by when the concepts it is advocating ended after the latest discoveries.

People Also Read: SAT Essay Cancellation: Before College Registration Process

Why most Professors want Recent Sources

Professor prefers the most recent sources because they have the most current and relevant information to support your topic and assignments. Besides, the recent sources carry the latest developments about the topic hence reliable for contribution and make your research work to be credible.

Besides, professors will prefer students to use the most current source to cite their work because they do not want their paper to have outdated, biased, or unreliable information thereby compromising the credibility of the research.

You should try to check the time when the journal came into publication to get the right information that your professor is seeking.

Also, the number of sources for a research paper matters. This is because the majority of the sources should be recent. Therefore, if you have many, the age of the sources will be a factor to balance them.

When not handling complex essays and academic writing tasks, Josh is busy advising students on how to pass assignments. In spare time, he loves playing football or walking with his dog around the park.

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References: How to Cite and List Correctly

First Online: 25 February 2021

Cite this chapter

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When we write an essay, research paper, thesis, or book, it is normal to include information from the work of others or support our arguments by reference to other published works. All such academic documents draw heavily on the ideas and findings of previous and current researchers available through various sources such as books, journals, theses, newspapers, magazines, government reports, or Internet sources. In all these cases, proper referencing is essential in order to ensure easy retrieval of information. Referencing is the name given to the method of showing and acknowledging the sources from which the author has obtained ideas or information.

Everything deep is also simple and can be reproduced simply as long as its reference to the whole truth is maintained. But what matters is not what is witty but what is true. Albert Schweitzer (1875–1965)

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A citation is a formal reference to a published or unpublished source that you consulted and obtained information from while writing your research paper. It refers to a source of information that supports a factual statement, proposition, argument, or assertion or any quoted text obtained from a book, article, web site, or any other type of material . In-text citations are embedded within the body of your paper and use a shorthand notation style that refers to a complete description of the item at the end of the paper. Materials cited at the end of a paper may be listed under the heading References, Sources, Works Cited, or Bibliography. Rules on how to properly cite a source depends on the writing style manual your professor wants you to use for the class [e.g., APA, MLA, Chicago, Turabian, etc.]. Note that some disciplines have their own citation rules [e.g., law].

Citations: Overview. OASIS Writing Center, Walden University; Research and Citation. The Writing Lab and The OWL. Purdue University; Citing Sources. University Writing Center, Texas A&M University.

Citing Your Sources

Reasons for Citing Sources in Your Research Paper

English scientist, Sir Isaac Newton, once wrote, "If I have seen further, it is by standing on the shoulders of giants.”* Citations support learning how to "see further" through processes of intellectual discovery, critical thinking, and applying a deliberate method of navigating through the scholarly landscape by tracking how cited works are propagated by scholars over time and the subsequent ways this leads to the devarication of new knowledge.

Listed below are specific reasons why citing sources is an important part of doing good research.

Shows the reader where to find more information . Citations help readers expand their understanding and knowledge about the issues being investigated. One of the most effective strategies for locating authoritative, relevant sources about a research problem is to review materials cited in studies published by other authors. In this way, the sources you cite help the reader identify where to go to examine the topic in more depth and detail.
Increases your credibility as an author . Citations to the words, ideas, and arguments of scholars demonstrates that you have conducted a thorough review of the literature and, therefore, you are reporting your research results or proposing recommended courses of action from an informed and critically engaged perspective. Your citations offer evidence that you effectively contemplated, evaluated, and synthesized sources of information in relation to your conceptualization of the research problem.
Illustrates the non-linear and contested nature of knowledge creation . The sources you cite show the reader how you characterized the dynamics of prior knowledge creation relevant to the research problem and how you managed to identify the contested relationships between problems and solutions proposed among scholars. Citations don't just list materials used in your study, they tell a story about how prior knowledge-making emerged from a constant state of creation, renewal, and transformation.
Reinforces your arguments . Sources cited in your paper provide the evidence that readers need to determine that you properly addressed the “So What?” question. This refers to whether you considered the relevance and significance of the research problem, its implications applied to creating new knowledge, and its importance for improving practice. In this way, citations draw attention to and support the legitimacy and originality of your own ideas and assertions.
Demonstrates that you "listened" to relevant conversations among scholars before joining in . Your citations tell the reader where you developed an understanding of the debates among scholars. They show how you educated yourself about ongoing conversations taking place within relevant communities of researchers before inserting your own ideas and arguments. In peer-reviewed scholarship, most of these conversations emerge within books, research reports, journal articles, and other cited works.
Delineates alternative approaches to explaining the research problem . If you disagree with prior research assumptions or you believe that a topic has been understudied or you find that there is a gap in how scholars have understood a problem, your citations serve as the source materials from which to analyze and present an alternative viewpoint or to assert that a different course of action should be pursued. In short, the materials you cite serve as the means by which to argue persuasively against long-standing assumptions promulgated in prior studies.
Helps the reader understand contextual aspects of your research . Cited sources help readers understand the specific circumstances, conditions, and settings of the problem being investigated and, by extension, how your arguments can be fully understood and assessed. Citations place your line of reasoning within a specific contextualized framework based on how others have studied the problem and how you interpreted their findings in support of your overall research objectives.
Frames the development of concepts and ideas within the literature . No topic in the social and behavioral sciences rests in isolation from research that has taken place in the past. Your citations help the reader understand the growth and transformation of the theoretical assumptions, key concepts, and systematic inquiries that emerged prior to your engagement with the research problem.
Underscores sources that were most important to you . Your citations represent a set of choices made about what you determined to be the most important sources for understanding the topic. They not only list what you discovered, but why it matters and how the materials you chose to cite fit within the broader context of your research design and arguments. As part of an overall assessment of the study’s validity and reliability , the choices you make also helps the reader determine what sources of research may have been excluded.
Provides evidence of interdisciplinary thinking . An important principle of good research is to extend your review of the literature beyond the predominant disciplinary space where scholars have previously examined a topic. Citations provide evidence that you have integrated epistemological arguments, observations, and/or methodological strategies of other disciplines into your paper, thereby demonstrating that you understand the complex, interconnected nature of contemporary research topics.
Forms the basis for bibliometric analysis of research . Bibliometric analysis is a quantitative method used, for example, to identify and predict emerging trends in research, document patterns of collaboration among scholars, explore the intellectual structure of a specific domain of research, map the development of research within and across disciplines, or identify gaps in knowledge within the literature. Bibliometrics data can also be used to visually map relationships among published studies. An author's citations to books, journal articles, research reports, and other publications represent the raw data used in bibliometric research.
Reveals possible adherence to the principles of citational justice. Citational justice refers to a movement within academe that....
Supports critical thinking and independent learning . Evaluating the authenticity, reliability, validity, and originality of prior research is an act of interpretation and introspective reasoning applied to assessing whether a source of information will contribute to understanding the problem in ways that are persuasive and align with your overall research objectives. Reviewing and citing prior studies represents a deliberate act of critically scrutinizing each source as part of your overall assessment of how scholars have confronted the research problem.
Honors the achievements of others . As Susan Blum recently noted,** citations not only identify sources used, they acknowledge the achievements of scholars within the larger network of research about the topic. Citing sources is a normative act of professionalism within academe and a way to highlight and recognize the work of scholars who likely do not obtain any tangible benefits or monetary value from their research endeavors. Your citations help to validate the work of others.

*Vernon. Jamie L. "On the Shoulder of Giants." American Scientist 105 (July-August 2017): 194.

**Blum, Susan D. "In Defense of the Morality of Citation.” Inside Higher Ed , January 29, 2024.

Aksnes, Dag W., Liv Langfeldt, and Paul Wouters. "Citations, Citation Indicators, and Research Quality: An Overview of Basic Concepts and Theories." Sage Open 9 (January-March 2019): https://doi.org/10.1177/2158244019829575; Blum, Susan Debra. My Word!: Plagiarism and College Culture . Ithaca, NY: Cornell University Press, 2009; Bretag, Tracey., editor. Handbook of Academic Integrity . Singapore: Springer Singapore, 2020; Ballenger, Bruce P. The Curious Researcher: A Guide to Writing Research Papers . 7th edition. Boston, MA: Pearson, 2012; D'Angelo, Barbara J. "Using Source Analysis to Promote Critical Thinking." Research Strategies 18 (Winter 2001): 303-309; Kwon, Diana. “The Rise of Citational Justice.” Nature 603 (March 24, 2022): 568-572; Donthu, Naveen et al. “How to Conduct a Bibliometric Analysis: An Overview and Guidelines.” Journal of Business Research 133 (2021): 285-296; Mauer, Barry and John Venecek. “Scholarship as Conversation.” Strategies for Conducting Literary Research, University of Central Florida, 2021; Öztürk, Oguzhan, Ridvan Kocaman, and Dominik K. Kanbach. "How to Design Bibliometric Research: An Overview and a Framework Proposal." Review of Managerial Science (2024): 1-29; Why Cite? Poorvu Center for Teaching and Learning, Yale University; Citing Information. The Writing Center. University of North Carolina; Harvard Guide to Using Sources. Harvard College Writing Program. Harvard University; Newton, Philip. "Academic Integrity: A Quantitative Study of Confidence and Understanding in Students at the Start of Their Higher Education." Assessment and Evaluation in Higher Education 41 (2016): 482-497; Referencing More Effectively. Academic Skills Centre. University of Canberra; Using Sources. Yale College Writing Center. Yale University; Vosburgh, Richard M. "Closing the Academic-practitioner Gap: Research Must Answer the “SO WHAT” Question." H uman Resource Management Review 32 (March 2022): 100633; When and Why to Cite Sources. Information Literacy Playlists, SUNY, Albany Libraries.

Structure and Writing Style

Referencing your sources means systematically showing what information or ideas you acquired from another author’s work, and identifying where that information come from . You must cite research in order to do research, but at the same time, you must delineate what are your original thoughts and ideas and what are the thoughts and ideas of others. Citations help achieve this. Procedures used to cite sources vary among different fields of study. If not outlined in your course syllabus or writing assignment, always speak with your professor about what writing style for citing sources should be used for the class because it is important to fully understand the citation style to be used in your paper, and to apply it consistently. If your professor defers and tells you to "choose whatever you want, just be consistent," then choose the citation style you are most familiar with or that is appropriate to your major [e.g., use Chicago style if you are majoring in history; use APA if its an education course; use MLA if it is literature or a general writing course].

GENERAL GUIDELINES

1. Are there any reasons I should avoid referencing other people's work? No. If placed in the proper context, r eferencing other people's research is never an indication that your work is substandard or lacks originality. In fact, the opposite is true. If you write your paper without adequate references to previous studies, you are signaling to the reader that you are not familiar with the literature on the topic, thereby, undermining the validity of your study and your credibility as a researcher. Including references in academic writing is one of the most important ways to demonstrate your knowledge and understanding of how the research problem has been addressed. It is the intellectual packaging around which you present your thoughts, ideas, and arguments to the reader.

2. What should I do if I find out that my great idea has already been studied by another researcher? It can be frustrating to come up with what you believe is a great topic only to find that it's already been thoroughly studied. However, do not become frustrated by this. You can acknowledge the prior research by writing in the text of your paper [see also Smith, 2002], then citing the complete source in your list of references. Use the discovery of prior studies as an opportunity to demonstrate the significance of the problem being investigated and, if applicable, as a means of delineating your analysis from those of others [e.g., the prior study is ten years old and doesn't take into account new variables]. Strategies for responding to prior research can include: stating how your study updates previous understandings about the topic, offering a new or different perspective, applying a different or innovative method of gathering and interpreting data, and/or describing a new set of insights, guidelines, recommendations, best practices, or working solutions.

3. What should I do if I want to use an adapted version of someone else's work? You still must cite the original work. For example, you use a table of statistics from a journal article published in 1996 by author Smith, but you have altered or added new data to it. Reference the revised chart, such as, [adapted from Smith, 1996], then cite the original source in your list of references. You can also use other terms in order to specify the exact relationship between the original source and the version you have presented, such as, "based on data from Smith [1996]...," or "summarized from Smith [1996]...." Citing the original source helps the reader locate where the information was first presented and under what context it was used as well as to evaluate how effectively you applied it to your own research.

4. What should I do if several authors have published very similar information or ideas? You can indicate that the topic, idea, concept, or information can be found in the works of others by stating something similar to the following example: "Though many scholars have applied rational choice theory to understanding economic relations among nations [Smith, 1989; Jones, 1991; Johnson, 1994; Anderson, 2003; Smith, 2014], little attention has been given to applying the theory to examining the influence of non-governmental organizations in a globalized economy." If you only reference one author or only the most recent study, then your readers may assume that only one author has published on this topic, or more likely, they will conclude that you have not conducted a thorough review of the literature. Referencing all relevant authors of prior studies gives your readers a clear idea of the breadth of analysis you conducted in preparing to study the research problem. If there has been a significant number of prior studies on the topic [i.e., ten or more], describe the most comprehensive and recent works because they will presumably discuss and reference the older studies. However, note in your review of the literature that there has been significant scholarship devoted to the topic so the reader knows that you are aware of the numerous prior studies.

5. What if I find exactly what I want to say in the writing of another researcher? In the social sciences, the rationale in duplicating prior research is generally governed by the passage of time, changing circumstances or conditions, or the emergence of variables that necessitate new investigations . If someone else has recently conducted a thorough investigation of precisely the same research problem that you intend to study, then you likely will have to revise your topic, or at the very least, review this literature to identify something new to say about the problem. However, if it is someone else's particularly succinct expression, but it fits perfectly with what you are trying to say, then you can quote from the author directly, referencing the source. Identifying an author who has made the exact same point that you want to make can be an opportunity to validate, as well as reinforce the significance of, the research problem you are investigating. The key is to build on that idea in new and innovative ways. If you are not sure how to do this, consult with a librarian .

6. Should I cite a source even if it was published long ago? Any source used in writing your paper should be cited, regardless of when it was written. However, in building a case for understanding prior research about your topic, it is generally true that you should focus on citing more recently published studies because they presumably have built upon the research of older studies. When referencing prior studies, use the research problem as your guide when considering what to cite. If a study from forty years ago investigated the same topic, it probably should be examined and considered in your list of references because the research may have been foundational or groundbreaking at the time, even if its findings are no longer relevant to current conditions or reflect current thinking [one way to determine if a study is foundational or groundbreaking is to examine how often it has been cited in recent studies using the "Cited by" feature of Google Scholar ]. However, if an older study only relates to the research problem tangentially or it has not been cited in recent studies, then it may be more appropriate to list it under further readings .

7. Can I cite unusual and non-scholarly sources in my research paper? The majority of the citations in a research paper should be to scholarly [a.k.a., academic; peer-reviewed] studies that rely on an objective and logical analysis of the research problem based on empirical evidence that reliably supports your arguments. However, any type of source can be considered valid if it brings relevant understanding and clarity to the topic. This can include, for example, non-textual elements such as photographs, maps, or illustrations. A source can include materials from special or archival collections, such as, personal papers, manuscripts, business memorandums, the official records of an organization, or digitized collections. Citations can also be to unusual items, such as, an audio recording, a transcript from a television news program, a unique set of data, or a social media post. The challenge is knowing how to cite unusual and non-scholarly sources because they often do not fit within consistent citation rules of books or journal articles. Given this, consult with a librarian if you are unsure how to cite a source.

NOTE: In any academic writing, you are required to identify which ideas, facts, thoughts, concepts, or declarative statements are yours and which are derived from the research of others. The only exception to this rule is information that is considered to be a commonly known fact [e.g., "George Washington was the first president of the United States"] or a statement that is self-evident [e.g., "Australia is a country in the Global South"]. Appreciate, however, that any "commonly known fact" or self-evidencing statement is culturally constructed and shaped by specific social and aesthetical biases . If you have any doubt about whether or not a fact is considered to be widely understood knowledge, provide a supporting citation, or, ask your professor for clarification about whether the statement should be cited.

Ballenger, Bruce P. The Curious Researcher: A Guide to Writing Research Papers . 7th edition. Boston, MA: Pearson, 2012; Blum, Susan Debra. My Word!: Plagiarism and College Culture . Ithaca, NY: Cornell University Press, 2009; Bretag, Tracey., editor. Handbook of Academic Integrity . Singapore: Springer Singapore, 2020; Carlock, Janine. Developing Information Literacy Skills: A Guide to Finding, Evaluating, and Citing Sources . Ann Arbor, MI: University of Michigan Press, 2020; Harvard Guide to Using Sources. Harvard College Writing Program. Harvard University; How to Cite Other Sources in Your Paper. The Structure, Format, Content, and Style of a Journal-Style Scientific Paper. Department of Biology. Bates College; Lunsford, Andrea A. and Robert Connors; The St. Martin's Handbook . New York: St. Martin's Press, 1989; Mills, Elizabeth Shown. Evidence Explained: Citing History Sources from Artifacts to Cyberspace . 3rd edition. Baltimore, MD: Genealogical Publishing Company, 2015; Research and Citation Resources. The Writing Lab and The OWL. Purdue University; Writing Tutorial Services, Center for Innovative Teaching and Learning. Indiana University; Why Cite? Poorvu Center for Teaching and Learning, Yale Univeraity.

Other Citation Research Guides

The following USC Libraries research guide can help you properly cite sources in your research paper:

Citation Guide

The following USC Libraries research guide offers basic information on using images and media in research:

Listed below are particularly well-done and comprehensive websites that provide specific examples of how to cite sources under different style guidelines.

Purdue University Online Writing Lab
Southern Cross University Harvard Referencing Style
University of Wisconsin Writing Center

This is a useful guide concerning how to properly cite images in your research paper.

Colgate Visual Resources Library, Citing Images

This guide provides good information on the act of citation analysis, whereby you count the number of times a published work is cited by other works in order to measure the impact of a publication or author.

Measuring Your Impact: Impact Factor, Citation Analysis, and other Metrics: Citation Analysis [Sandy De Groote, University of Illinois, Chicago]

Automatic Citation Generators

The links below lead to systems where you can type in your information and have a citation compiled for you. Note that these systems are not foolproof so it is important that you verify that the citation is correct and check your spelling, capitalization, etc. However, they can be useful in creating basic types of citations, particularly for online sources.

BibMe -- APA, MLA, Chicago, and Turabian styles
DocsCite -- for citing government publications in APA or MLA formats
EasyBib -- APA, MLA, and Chicago styles
Son of Citation Machine -- APA, MLA, Chicago, and Turabian styles

NOTE: Many companies that create the research databases the USC Libraries subscribe to, such as ProQuest , include built-in citation generators that help take the guesswork out of how to properly cite a work. When available, you should always utilize these features because they not only generate a citation to the source [e.g., a journal article], but include information about where you accessed the source [e.g., the database].

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How Old Sources for References and Literature Review should be

How Old essay Sources should be

For many students, the question of how old or how recent the references should be in a paper is often confusing. In this comprehensive guide, we explore the age of your sources for a literature review or arguments in your paper, essay, thesis, or dissertation.

The issue of the recency of sources comes up because, in most cases, instructors fail to teach their students about referencing when it comes to their relevance and age.

Instructors focus more on how students should structure or organize their references as per academic conventions of writing formats such as MLA, APA, Chicago, Harvard, and so on.

How Old should your References be in a Paper?

The age of your references in a research paper should not be older than 5 years old unless otherwise stated. This applies where possible, as some papers require older sources.

Using recent sources gives you updated information, which improves your paper’s credibility and affirms the authoritativeness of your arguments.

However, this depends on the type of paper and its discipline. In some papers, you can use older references. For example, imagine your paper’s topic is the Cold War.

In such a topic, you can use references from the 1980s and 90s because the issue of the Cold War was particularly explored by scholars when it was occurring.

On the other hand, imagine you are writing about the socio-economic impact of Trump’s presidency in the United States. In such a topic, you will strictly use references of not more than 4 years because Donald Trump became president about 4 years ago.

From the examples above, it is evident that the paper’s nature and the context to be written will determine how old the references will be.

The point here is that you should know the type of paper you are going to write so that you can determine the age of the references to be used. Though this is the case, you should avoid references older than 6 years when writing a paper.

Combining the Age of Sources for Some Papers

Some papers require old sources, while other essays require recent sources. Also, some instructors are more lenient regarding the age of references used, while others are strict.

In that case, you can comfortably combine both old sources with the most recent ones. The content and context of the paper also determine how old the references should be.

For example, imagine being given a topic concerning the economic impact of COVID-19 in the United States, and you are required to come up with a 5-page paper.

Since this will be a research paper, you will use peer-reviewed sources to support your arguments and provide actual facts and statistics to reinforce the arguments.

In such a case, your sources will be as recent as the current month of 2020 because this is the year when the disease became a global pandemic.

You cannot use references older than that to support your arguments.

For historical papers, students can use older references because historical events are past documentation of occurrences that cannot be altered.

This is a straightforward example to demonstrate the importance of using relevant and age-appropriate references. The following sections discuss this issue in detail.

How recent should your references be in a paper?

Your references for your papers and essays should be as recent as possible and within 5 years of publishing. However, the topic of your paper determines how recent your paper should be. Through the references can be as recent as the year you are writing the paper.

This especially applies to topics that are based on current issues or trends. For example, topics revolving around COVID-19 fall under current issues, and therefore references as old as a few days from the time you are writing the paper can be used.

However, topics that are not centered on current issues should not use references that are extremely recent, like a few days old.

This is because the source has not had enough time to be analyzed by more scholars who could disapprove of the arguments or findings of the source material based on their scholarly approaches and research.

Read more on this issue in our guide on how old references should be so that you can learn in detail and get the factors involved.

Factors to Consider when Determining the Age of your References

One of the most important factors to consider when determining the recency of references is the year they were written.

In any piece of writing, the author(s) provide their names and the year, at times, the month and day they wrote it.

In scholarly writings, the name of the author(s) and the year of publication is always provided. Therefore, when determining the recency of references, look for the year the source was published.

The second factor to consider when determining the recency of references is the topic or the issues that are discussed within the source material.

As aforementioned, papers can discuss recent or trending issues, while others can discuss historical issues. If the topic of the source material covers recent issues, then the reference is recent.

On the other hand, if the topic discusses past or historical issues, then there is a great probability that the reference is old.

Finally, the writing and/or academic conventions used to create the source material determines the recency of references. Writing and academic conventions are constantly evolving.

The methods used to write and reference different types of papers, like APA, Harvard, and so on, have been changing.

Therefore, sources that use outdated writing and referencing conventions are old, while those using the latest conventions are the most recent.

How Old Should Literature be in a Literature Review?

Now that we have discussed the reason behind the question of how old your references should be let us delve into more detail concerning literature in literature review.

Ideally, the literature in a literature review should not be more than 5 years old from the time of publishing to when you are using it as a source for your essay, paper, thesis, or dissertation. However, this depends on the available resources and the topic you are writing on.

While some topics have so many sources of information, others are so recent and have fewer sources in the library to depend on. Therefore, consider a well-resourced topic when selecting it before writing the literature review.

As the name suggests, the literature review is the process of analyzing a particular topic from a critical point of view.

This means you will use various secondary literature to help support your claims within the literature review. This also depends on the type of paper you are writing.

There are different types of papers, and each paper utilizes a set of rules when it comes to referencing. Let us explore the age of the sources needed to write a paper.

Reasons for Using Recent Sources

One of the reasons behind this is centered on the literature review itself. What is the topic to be discussed? The literature review explores the current knowledge concerning the topic.

If other writers have explored the same topic, then it means that they have refined their findings because they have been building upon other writers’ works.

Therefore, it is imperative to use the most recent literature during a literature review. The more recent the literature, the more accurate its findings will be.

Another reason for using the most recent literature during the literature review is that older claims can be dismissed by recent claims.

Research is important because it helps us to understand the underlying factors that cause something.

If, for example, an author presented a claim 10 years ago, another author may dismiss the claim after a few years because of further research.

This is the reason why it is imperative to use the most recent literature to provide current knowledge concerning the topic.

What comes first; the Relevance or the Age of Essay Sources?

The answer to this question depends on the paper’s requirements. However, the relevance of the sources should come first. Relevance is defined as the relation of something to the matter at hand.

Therefore, if the sources are used to provide relevant and credible content about your topic, then their age does not matter. What matters is the credibility and applicability of the source’s information to your essay.

Though this is the case, some instructors will only accept the most recent sources because they provide current research concerning the topic at hand.

In such cases, it is best to provide the most recent sources while still considering their relevance.

However, there are some old sources that are used because of their authority. There are aged, highly cited old papers, and the reason why they are used is because of their source.

What should be noted is that while you will be required to provide recent sources in most of your papers, it is imperative to consider the relevance of those sources first. Not all sources are relevant to the topic at hand.

Final Advice

To conclude, we will advise you to consult your instructor and know his or her expectations concerning the age of your sources.

If instructors tackle this question with their students, then the issue of students using irrelevant references or references that are considered too old would not be rampant.

Jessica Smart

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How to write a Theory of Knowledge (TOK) Essay: Full Guide

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Knowledge Base
Citing sources

How to Cite Sources | Citation Generator & Quick Guide

Citing your sources is essential in academic writing . Whenever you quote or paraphrase a source (such as a book, article, or webpage), you have to include a citation crediting the original author.

Failing to properly cite your sources counts as plagiarism , since you’re presenting someone else’s ideas as if they were your own.

The most commonly used citation styles are APA and MLA. The free Scribbr Citation Generator is the quickest way to cite sources in these styles. Simply enter the URL, DOI, or title, and we’ll generate an accurate, correctly formatted citation.

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When do you need to cite sources, which citation style should you use, in-text citations, reference lists and bibliographies.

Scribbr Citation Generator

Other useful citation tools

Citation examples and full guides, frequently asked questions about citing sources.

Citations are required in all types of academic texts. They are needed for several reasons:

To avoid plagiarism by indicating when you’re taking information from another source
To give proper credit to the author of that source
To allow the reader to consult your sources for themselves

A citation is needed whenever you integrate a source into your writing. This usually means quoting or paraphrasing:

To quote a source , copy a short piece of text word for word and put it inside quotation marks .
To paraphrase a source , put the text into your own words. It’s important that the paraphrase is not too close to the original wording. You can use the paraphrasing tool if you don’t want to do this manually.

Citations are needed whether you quote or paraphrase, and whatever type of source you use. As well as citing scholarly sources like books and journal articles, don’t forget to include citations for any other sources you use for ideas, examples, or evidence. That includes websites, YouTube videos , and lectures .

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Usually, your institution (or the journal you’re submitting to) will require you to follow a specific citation style, so check your guidelines or ask your instructor.

In some cases, you may have to choose a citation style for yourself. Make sure to pick one style and use it consistently:

APA Style is widely used in the social sciences and beyond.
MLA style is common in the humanities.
Chicago notes and bibliography , common in the humanities
Chicago author-date , used in the (social) sciences
There are many other citation styles for different disciplines.

If in doubt, check with your instructor or read other papers from your field of study to see what style they follow.

In most styles, your citations consist of:

Brief in-text citations at the relevant points in the text
A reference list or bibliography containing full information on all the sources you’ve cited

In-text citations most commonly take the form of parenthetical citations featuring the last name of the source’s author and its year of publication (aka author-date citations).

An alternative to this type of in-text citation is the system used in numerical citation styles , where a number is inserted into the text, corresponding to an entry in a numbered reference list.

There are also note citation styles , where you place your citations in either footnotes or endnotes . Since they’re not embedded in the text itself, these citations can provide more detail and sometimes aren’t accompanied by a full reference list or bibliography.

(London: John Murray, 1859), 510.

A reference list (aka “Bibliography” or “Works Cited,” depending on the style) is where you provide full information on each of the sources you’ve cited in the text. It appears at the end of your paper, usually with a hanging indent applied to each entry.

The information included in reference entries is broadly similar, whatever citation style you’re using. For each source, you’ll typically include the:

Author name
Publication date
Container (e.g., the book an essay was published in, the journal an article appeared in)
Location (e.g., a URL or DOI , or sometimes a physical location)

The exact information included varies depending on the source type and the citation style. The order in which the information appears, and how you format it (e.g., capitalization, use of italics) also varies.

Most commonly, the entries in your reference list are alphabetized by author name. This allows the reader to easily find the relevant entry based on the author name in your in-text citation.

In numerical citation styles, the entries in your reference list are numbered, usually based on the order in which you cite them. The reader finds the right entry based on the number that appears in the text.

Because each style has many small differences regarding things like italicization, capitalization , and punctuation , it can be difficult to get every detail right. Using a citation generator can save you a lot of time and effort.

Scribbr offers citation generators for both APA and MLA style. Both are quick, easy to use, and 100% free, with no ads and no registration required.

Just input a URL or DOI or add the source details manually, and the generator will automatically produce an in-text citation and reference entry in the correct format. You can save your reference list as you go and download it when you’re done, and even add annotations for an annotated bibliography .

Once you’ve prepared your citations, you might still be unsure if they’re correct and if you’ve used them appropriately in your text. This is where Scribbr’s other citation tools and services may come in handy:

Plagiarism Checker

Citation Checker

Citation Editing

Plagiarism means passing off someone else’s words or ideas as your own. It’s a serious offense in academia. Universities use plagiarism checking software to scan your paper and identify any similarities to other texts.

When you’re dealing with a lot of sources, it’s easy to make mistakes that could constitute accidental plagiarism. For example, you might forget to add a citation after a quote, or paraphrase a source in a way that’s too close to the original text.

Using a plagiarism checker yourself before you submit your work can help you spot these mistakes before they get you in trouble. Based on the results, you can add any missing citations and rephrase your text where necessary.

Try out the Scribbr Plagiarism Checker for free, or check out our detailed comparison of the best plagiarism checkers available online.

Scribbr Plagiarism Checker

Scribbr’s Citation Checker is a unique AI-powered tool that automatically detects stylistic errors and inconsistencies in your in-text citations. It also suggests a correction for every mistake.

Currently available for APA Style, this is the fastest and easiest way to make sure you’ve formatted your citations correctly. You can try out the tool for free below.

If you need extra help with your reference list, we also offer a more in-depth Citation Editing Service.

Our experts cross-check your in-text citations and reference entries, make sure you’ve included the correct information for each source, and improve the formatting of your reference page.

If you want to handle your citations yourself, Scribbr’s free Knowledge Base provides clear, accurate guidance on every aspect of citation. You can see citation examples for a variety of common source types below:

And you can check out our comprehensive guides to the most popular citation styles:

At college level, you must properly cite your sources in all essays , research papers , and other academic texts (except exams and in-class exercises).

Add a citation whenever you quote , paraphrase , or summarize information or ideas from a source. You should also give full source details in a bibliography or reference list at the end of your text.

The exact format of your citations depends on which citation style you are instructed to use. The most common styles are APA , MLA , and Chicago .

The abbreviation “ et al. ” (Latin for “and others”) is used to shorten citations of sources with multiple authors.

“Et al.” is used in APA in-text citations of sources with 3+ authors, e.g. (Smith et al., 2019). It is not used in APA reference entries .

Use “et al.” for 3+ authors in MLA in-text citations and Works Cited entries.

Use “et al.” for 4+ authors in a Chicago in-text citation , and for 10+ authors in a Chicago bibliography entry.

The Scribbr Citation Generator is developed using the open-source Citation Style Language (CSL) project and Frank Bennett’s citeproc-js . It’s the same technology used by dozens of other popular citation tools, including Mendeley and Zotero.

You can find all the citation styles and locales used in the Scribbr Citation Generator in our publicly accessible repository on Github .

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Open Access

Ten simple rules for responsible referencing

* E-mail: [email protected]

Affiliation Maastricht University, Care and Public Health Research Institute (CAPHRI), Department of Health, Ethics & Society, Maastricht, the Netherlands

Bart Penders

Published: April 12, 2018

https://doi.org/10.1371/journal.pcbi.1006036
Reader Comments

Citation: Penders B (2018) Ten simple rules for responsible referencing. PLoS Comput Biol 14(4): e1006036. https://doi.org/10.1371/journal.pcbi.1006036

Editor: Scott Markel, Dassault Systemes BIOVIA, UNITED STATES

Copyright: © 2018 Bart Penders. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Funding: The work that lead to this publication was, in part, supported by the ZonMW programme Fostering Responsible Research Practices, grant no. 45001005. The funder had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

We researchers aim to read and write publications containing high-quality prose, exceptional data, arguments, and conclusions, embedded firmly in existing literature while making abundantly clear what we are adding to it. Through the inclusion of references, we demonstrate the foundation upon which our studies rest as well as how they are different from previous work. That difference can include literature we dispute or disprove, arguments or claims we expand, and new ideas, suggestions, and hypotheses we base upon published work. This leads to the question of how to decide which study or author to cite, and in what way.

Writing manuscripts requires, among so much more, decisions on which previous studies to include and exclude, as well as decisions on how exactly that inclusion takes place. A well-referenced manuscript places the authors’ argument in the proper knowledge context and thereby can support its novelty, its value, and its visibility. Citations link one study to others, creating a web of knowledge that carries meaning and allows other researchers to identify work as relevant in general and relevant to them in particular.

On the one hand, citation practices create value by tying together relevant scientific contributions, regardless of whether they are large or small. In the process, they confer or withhold credit, contributing to the relative status of published work in the literature. On the other hand, citation practices exist in the context of current regimes of evaluating science. While it may go unnoticed in daily writing practices, the act of including a single reference in a study is thus subject to value-based criteria internal to science (e.g., content, relevance, credit) and external to science (e.g., accountability, performance).

Accordingly, referencing is not a neutral act. Citations are a form of scientific currency, actively conferring or denying value. Citing certain sources—and especially citing them often—legitimises ideas, solidifies theories, and establishes claims as facts. References also create transparency by allowing others to retrace your steps. Referencing is thus a moral issue, an issue upon which multiple values in science converge. Citing competitors adds to their profiles, citing papers from a specific journal adds to its impact factor, citing supervisors or lab mates helps build your own profile, and citing the right papers helps establish your familiarity with the field. All of these translate into pressures on scientists to cite specific sources, from peers, editors, and others. Fong and Wilhite demonstrate the abundance of so-called coercive citation practices [ 1 ]. Also, citation-based metrics have proliferated as proxies for quality and impact over the years [ 2 – 4 ], only to be currently subjected to significant and highly relevant critique [ 5 – 8 ]. To cite well, or to reference responsibly, is thus a matter of concern to all scientists.

Here, I offer 10 simple rules for responsible referencing. Scientists as authors produce references, and as readers and reviewers, they assess and evaluate references. Through this symmetrical relationship to literature that all scientists share, they take responsibility for tying together all knowledge it contains. Producing and evaluating references are, however, distinct processes, warranting different responsibilities. Respecting this dual relationship researchers have with literature, the first six rules primarily refer to producing a citation and the responsibilities this entails. The second set of four rules refers to evaluating citations and the meaning they have or acquire once they have become part of a text.

Rule 1: Include relevant citations

All scholarly writing requires a demonstration of the relevance of the questions asked, a display of the methods used, a rationale for the use of materials, and a discussion of issues relevant to the content of the publication. All of these are done, at least in large part, by including citations to relevant previous work. Omitting such references can wrongfully suggest that your own publication is the origin of an idea, a question, a method, or a critique, thereby illegitimately appropriating them. Citations identify where ideas have come from, and consulting the cited works allows readers of your text to study them more closely, as well as to evaluate whether your use of them is appropriate.

A single exception exists when facts, findings, or methods have become part of scientific or scholarly canon. There is no need to include a citation on the claim that DNA is built out of four bases, nor do you have to cite Kjell Kleppe or Kary Mullis every time you use PCR (neither do I right now). However, the decision as to when something truly becomes part of canon can be quite difficult and will include periods of adjustment (with irregular citation) and negotiation (on whether to cite or not).

Rule 2: Read the publications you cite

Citation is not an administrative task. First, a single paper can be cited for multiple reasons, ranging from reported data to methods, and can be cited both positively and negatively in the literature. The only way to identify whether its content is relevant as support for your claim is to read it in full.

Second, the collection of citations included to support your work and argument is one of the elements from which your work draws credibility. The same goes for the citations you include to criticise, dispute, or disprove. As a consequence, a chain is only as strong as its weakest link. The quality of the publication you trust and upon which you confer authority codetermines the quality and credibility of your work. Citation rates, especially on the journal level, do not correspond well to research quality [ 9 ], and they conflate positive and negative citations, not distinguishing authority conferred or authority that is challenged. To cite meaningfully and credibly requires that you consult the content of a publication rather than whether others have cited it, as a criterion for citation.

Rule 3: Cite in accordance with content

If, at some phase in the research, you have decided that a specific study merits citation, the issue of specifically how and where to cite it deserves explicit consideration. Mere inclusion does not suffice. Sources deserve credit for the exact contribution they offer, not their contribution in general. This may mean that you need to cite a single source multiple times throughout your own argument, including explanations or indications why.

A specific way to break Rule 3 is in the form of the so-called ‘Trojan citation’ [ 10 ]. The Trojan citation arises when a publication reporting similar findings to your own is cited in the context of a discussion of a minor issue, ignoring (sometimes deliberately) its key argument or contribution. By focussing on a trivial detail, the Trojan citation obscures the true significance of the cited work. As a consequence, it hides that your work is not as novel as it seems. As a questionable citation practice, a Trojan citation can be used to satisfy reviewers’ or editors’ requests to include a reference to a relevant paper. Alternatively, a Trojan citation may emerge unknowingly when (1) you are unaware of the content of a cited publication (not adhering to Rule 2 creates a very significant risk of being unable to follow Rule 3) or (2) disputes exist in the scientific community or among the authors on the contribution and/or quality of a scientific publication (in which case, Rule 4 will help).

Rule 4: Cite transparently, not neutrally

Citing, even in accordance with content, requires context. This is especially important when it happens as part of the article’s argument. Not all citations are a part of an article’s argument. Citations to data, resources, materials, and established methods require less, if any, context. As part of the argument, however, the mere inclusion of a citation, even when in the right spot, does not convey the value of the reference and, accordingly, the rationale for including it. In a recent editorial, the Nature Genetics editors argued against so-called neutral citation. This citation practice, they argue, appears neutral or procedural yet lacks required displays of context of the cited source or rationale for including [ 11 ]. Rather, citations should mention assessments of value, worth, relevance, or significance in the context of whether findings support or oppose reported data or conclusions.

This flows from the realisation that citations are political, even though that term is rarely used in this context. Researchers can use them to accurately represent, inflate, or deflate contributions, based on (1) whether they are included and (2) whether their contributions are qualified. Context or rationale can be qualified by using the right verbs. The contribution of a specific reference can be inflated or deflated through the absence of or use of the wrong qualifying term (‘the authors suggest’ versus ‘the authors establish’; ‘this excellent study shows’ versus ‘this pilot study shows’). If intentional, it is a form of deception, rewriting the content of scientific canon. If unintentional, it is the result of sloppy writing. Ask yourself why you are citing prior work and which value you are attributing to it, and whether the answers to these questions are accessible to your readers.

Rule 5: Cite yourself when required

In the context of critical discussions of citations and evaluations of citation-based metrics, self-citation has almost become a taboo. It is important to realise, though, that self-citation serves an important function by showing incremental iterative advancement of your work [ 12 ]. As a consequence, your previous work or that of the group in which you are embedded should be cited in accordance with all of the rules above. The amount of acceptable self-citation is very likely to differ between fields; smaller fields (niche fields) are likely to (legitimately) exhibit more.

This does not mean that self-citation is always unproblematic. For instance, excessive self-citation can suggest salami slicing, a publication strategy in which elements of a single study are published separately [ 13 ]. This questionable research practice, in tandem with self-citation, aims to inflate publication and citation metrics.

Rule 6: Prioritise the citations you include

Many journals have restrictions on the number of references authors are allowed to include. The exact number varies per publisher, journal, and article type and can be as low as three (for a correspondence item in Nature ). Even if no reference limit exists, other journals impose a word limit that includes references, effectively also capping the amount of references. Coping with these limits sometimes requires difficult decisions to omit citations you may feel are legitimate or even necessary. In order to deal with this issue and avoid random removal of references, all desired citations require prioritisation. A few rules of thumb, shown in Box 1 , will help decisions on reference priority.

Box 1: Reference prioritisation

‘Ten simple sub-rules for prioritising references’ can help to facilitate prioritisation. In most cases, a subset of the 10 sub-rules will suffice. First, prioritise anew for each publication. Prioritisations cannot (easily) be copied from one study to another. Second, prioritise per section (e.g., introduction, methods, discussion), not across the entire paper. Different sections require different types of support. Third, for the introduction, prioritise reviews, allowing broad context for relevance and aim. Fourth, for the discussion, prioritise empirical papers, allowing detailed accounts of relative contribution. Fifth, prioritise reviewed over un- or prereviewed papers (e.g., editorials, preprints, etc.). Sixth, deprioritise self-citations. Seventh, limit the number of citations to support a specific claim, if necessary, to a single citation. Eighth, move methodological citations to supplementary (online) information. Ninth, in cases of equal relevance, prioritise citation of female first or last authors to help repair gender imbalances in science. Tenth, request the inclusion of additional references with the editors, arguing that you have used all of the previous nine sub-rules.

Rule 7: Evaluate citations as the choices that they are

Research publications are not mere vessels of data or findings. They convey a narrative explaining why questions are worth asking, what their answers may mean, how these answers were reached, why they are to be trusted, and more. They also have a purpose in the sense that they will act as support for other studies to come. Each of the elements of their story is supported by links to other studies, and each of those links is the result of an active choice by the author(s) in the context of the goal they wish to achieve by their inclusion.

At the other end of the narrative, readers assess and evaluate the story constantly, asking whether it could have been told differently. The realisation that narratives can be told differently, supported by other citations to other prior work, does not disqualify them. Both the story and the choice of citations are political choices meant to provide the argument with as much power, credibility, and legitimacy the author(s) can muster. They are tailored to the audience the authors seek to convince: their peers. The choice to include or exclude a reference can only be evaluated in the context of that narrative and the role they play in it. Peritz has provided a classification of citation roles to assist this evaluation [ 14 ].

Rule 8: Evaluate citations in their rhetorical context

Rhetorical strategies serve to convince and persuade. Narratives are but one of the tools that can be used to persuade audiences. Metaphors, numbers, and associations all feature in our research papers as tools to convince our readers. The genre of the scientific article has had centuries to evolve to incorporate many of them, with the goal of convincing readers that the author is right. Bazerman has literally written the book on this [ 15 ] and urges us to consider academic texts and their features as part of social and intellectual endeavours. Citations are a part of the social fabric of science in the sense that through citing specific sources, authors show their allegiance to schools of thought, communities, or, in the context of scientific controversies, which paradigm they consider themselves part of. Other rhetorical uses of citations include explicit citations to notable figures and their work, which can serve as appeals to authority, while long lists of citations can serve as proxies for well-studied subjects.

Consider the following: Authors can describe a field as well-studied and include three references—X, Y, and Z—as support for their claim. Alternatively, they can argue that a field is understudied but that three exceptions exist, i.e., X, Y, and Z. Understanding the value attributed to X, Y, and Z in that particular text requires assessment of the rhetorical strategies of the author(s).

Rule 9: Evaluate citations as framed communication

Authors use words to accomplish things and, in service of those goals, position their work and that of others. They frame prior work in a very specific way, supporting the arguments made. We all do. The positioning of X, Y, and Z either as the norm or as exceptions, as shown in Rule 8, is an example of framing. It is important to recognise such framing and that X, Y, and Z acquire meaning in the text as the result of the frame. There is no frameless communication, as Goffman [ 16 ] demonstrated. All messages and texts contain and require a frame—a structure of definitions and assumptions that help organise coherence, connections, and, ultimately, meaning—or in other words, a perspective on reality.

As a result, a citation is not a neutral line drawn between publications A and B. Rather, the representation of cited article A only acquires meaning in the context of citing in article B. Article A can be framed differently when cited in work B or C. It can be framed as innovative in B or dogmatic in C. Framing usually is not lying or deceiving; it is a normative positioning of evidence in context. Hence, a citation is a careful translation of a source’s relevant elements, which acquire meaning in that context only.

An important consequence of this is that merely counting citations of article A in the literature does not inform us of the value (or many types of value or lack thereof) of article A to the scientific community. This point also appears as the first principle in the Leiden Manifesto, which argues that quantitative metrics can only support qualitative metrics (i.e., reading with an attentive eye for politics, rhetoric, context, and frame—or as adhering to Rules 7–9). The Leiden Manifesto was published by bibliometricians and scholars of research evaluation following the 2014 conference on Science and Technology Indicators in Leiden, the Netherlands. It warns against the abuse of, among other things, citation-based research metrics [ 9 ].

Rule 10: Accept that citation cultures differ across boundaries

Despite critiques of the system, science is organised in such a way that citations continue to act as a currency that is represented as being universal [ 4 ]. However, citation practices are, for the most part, local practices, whether local to laboratories or department or local to disciplines. The average number of citations per paper differs between disciplines, and the way that citations are represented in the text and the value of being cited also differ radically [ 17 ]. What counts as proper citation practice in molecular biology—for instance, the inclusion of multiple references following a statement—is considered unacceptable in research ethics or science policy, in which single references require paragraphs of contextualisation and translation (see Rule 9 ). When reading a paper from an adjacent discipline, respect its different norms and conventions for responsible referencing and proper citation. If you are cited by a scientist from another discipline, assess that act as existing in a (however slightly) different citation culture.

Acknowledgments

I thank Maurice Zeegers and his team, who work on citation analyses, for stimulating me to think about the issue of citation more clearly, deeply, and critically, resulting in the considerations above. I also thank David Shaw for critical comments, moral support, and editorial assistance. As a closing note, as the human being that I am, I too have quite possibly referenced imperfectly in my previous work.

View Article
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3. Garfield E, Merton R. Citation indexing: Its theory and application in science, technology, and humanities: New York: Wiley; 1979.
4. Wouters P. The citation culture. Amsterdam: University of Amsterdam; 1999.
5. Dahler-Larsen P. Constitutive effects of performance indicator systems. Dilemmas of engagement: Evaluation and the new public management. Emerald Group Publishing Limited; 2007. p. 17–35.
15. Bazerman C. Shaping written knowledge: The genre and activity of the experimental article in science. Madison, WI: University of Wisconsin Press; 1988.
16. Goffman E. Frame analysis: An essay on the organization of experience.Cambrdige, MA: Harvard University Press; 1974.

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Reference List: Basic Rules

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This resourse, revised according to the 7 th edition APA Publication Manual, offers basic guidelines for formatting the reference list at the end of a standard APA research paper. Most sources follow fairly straightforward rules. However, because sources obtained from academic journals carry special weight in research writing, these sources are subject to special rules . Thus, this page presents basic guidelines for citing academic journals separate from its "ordinary" basic guidelines. This distinction is made clear below.

Note: Because the information on this page pertains to virtually all citations, we've highlighted one important difference between APA 6 and APA 7 with an underlined note written in red. For more information, please consult the Publication Manual of the American Psychological Association , (7 th ed.).

Formatting a Reference List

Your reference list should appear at the end of your paper. It provides the information necessary for a reader to locate and retrieve any source you cite in the body of the paper. Each source you cite in the paper must appear in your reference list; likewise, each entry in the reference list must be cited in your text.

Your references should begin on a new page separate from the text of the essay; label this page "References" in bold, centered at the top of the page (do NOT underline or use quotation marks for the title). All text should be double-spaced just like the rest of your essay.

Basic Rules for Most Sources

All lines after the first line of each entry in your reference list should be indented one-half inch from the left margin. This is called hanging indentation.
All authors' names should be inverted (i.e., last names should be provided first).
For example, the reference entry for a source written by Jane Marie Smith would begin with "Smith, J. M."
If a middle name isn't available, just initialize the author's first name: "Smith, J."
Give the last name and first/middle initials for all authors of a particular work up to and including 20 authors ( this is a new rule, as APA 6 only required the first six authors ). Separate each author’s initials from the next author in the list with a comma. Use an ampersand (&) before the last author’s name. If there are 21 or more authors, use an ellipsis (but no ampersand) after the 19th author, and then add the final author’s name.
Reference list entries should be alphabetized by the last name of the first author of each work.
For multiple articles by the same author, or authors listed in the same order, list the entries in chronological order, from earliest to most recent.
Note again that the titles of academic journals are subject to special rules. See section below.
Italicize titles of longer works (e.g., books, edited collections, names of newspapers, and so on).
Do not italicize, underline, or put quotes around the titles of shorter works such as chapters in books or essays in edited collections.

Basic Rules for Articles in Academic Journals

Present journal titles in full.
Italicize journal titles.
For example, you should use PhiloSOPHIA instead of Philosophia, or Past & Present instead of Past and Present.
This distinction is based on the type of source being cited. Academic journal titles have all major words capitalized, while other sources' titles do not.
Capitalize the first word of the titles and subtitles of journal articles , as well as the first word after a colon or a dash in the title, and any proper nouns .
Do not italicize or underline the article title.
Deep blue: The mysteries of the Marianas Trench.
Oceanographic Study: A Peer-Reviewed Publication

Please note: While the APA manual provides examples of how to cite common types of sources, it does not cover all conceivable sources. If you must cite a source that APA does not address, the APA suggests finding an example that is similar to your source and using that format. For more information, see page 282 of the Publication Manual of the American Psychological Association , 7 th ed.

When is the evidence too old?

A few weeks ago, when submitting an abstract to a nursing conference, I was suddenly faced with a dilemma about age. Not my own age, but the age of evidence I was using to support my work. One key element of the submission criteria was to provide five research citations to support the abstract, and all citations were to be less than ten years old. This requirement left me stumped for a while. The research I wanted to cite was more than ten years old, yet it was excellent research within a very small body of work on the topic. Suddenly I struggled to meet the criteria and almost gave up on the submission, thinking my abstract would not tick all of the boxes if I used research now deemed to be ‘out of date’. I suddenly thought about all of the work I had published more than ten years ago – all that hard work past its use-by date.

Way back in the mid 1990s, a colleague and I started to have conversations with Australian nurses about the importance of evidence based practice (EBP) for the future of Australian nursing. The movement away from the comfort of ‘ritual and routine’ to the uncertainty of EBP was challenging. At the time we described EBP according to the principle that “all interventions should be based on the best currently available scientific evidence” 1 . We had embraced the ideas of authors such as Ian Chalmers 2 and were keen to educate nurses and nursing students about “practices that had been clearly shown to work and question practices for which no evidence exists and discard those which have been shown to do harm” 1 It was very much about the importance of using the most ‘robust’ and ‘reliable’ evidence that we had available to guide us in clinical decision making, taking into account individual patients at the centre of care. It was also about teaching nurses and nursing students about how to ask the right questions, where to look for answers and how to recognize when you have found the right answer to support individualized patient care.

Definitions of evidence-based practice are quite varied and I have heard nurses talk about using “current best evidence” while others use the “most current evidence”. These are quite different approaches, with the latter statement suggesting that more recent is best. This is sometimes reinforced in nursing education, where students are graded according to the use of recent research, with limitations placed on the age of resources used to support their work. However, I wonder if we are losing something in this translation about the meaning of ‘best evidence’ to support care. When does the published evidence get too old and where do we draw the line and stop reading research from our past?

Personally I have always expected my students to use up to date research when supporting their recommendations for care. However, I have also encouraged them to look back to see where the new research has come from and to acknowledge the foundation it has been built on. I am always keen to hear about the latest developments in healthcare and work to support the readers of EBN who need and want to know about what is new and important in the health care literature. Keeping up to date with new evidence is critically important for change. But I wonder how we strike a balance between absorbing recent research and taking into account robust research that preceded its publication by more than a decade?

So, let’s think about these ideas for a minute. If we put our blinkers on and ignore important research from the recently ‘outdated’ literature from the 1990s (when I first became interested in doing research), we could miss some important foundational work that still influences practice today. The two references I have used below, both from the 1990s, would not be included in the discussion at all. If we only consider literature that is recent, and value that more highly than if it is robust, then we will be missing important evidence to inform practice. Researchers could start asking the same research questions over and over (I have seen some of this already in nursing literature) and even feel pressured to repeat previous studies all over again to check if the findings still hold true in the contemporary world. Perhaps that is something to watch for in the future.

It is important to keep up to date with current research findings, new innovations in care, recent trends in patient problems, trends in patient outcomes and changes in the social, political and system context of the care we provide. But it is also important to look back as we move forward, thinking about the strength of the evidence as well as its age.

Allison Shorten RN RM PhD

Yale University School of Nursing

References:

Shorten A. & Wallace MC. ‘Evidence-based practice – The future is clear’. Australian Nurses Journal, 1996, Vol. 4, No. 6, pp. 22-24.
Chalmers I. The Cochrane collaboration: Preparing, maintaining, and disseminating systematic reviews of the effects of health care, Annals New York Academy of Science, 1993, Vol. 703, pp. 156-165.

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Referencing

Referencing explained

Why and when to reference.

Referencing is an important part of academic work. It puts your work in context, demonstrates the breadth and depth of your research, and acknowledges other people’s work. You should reference whenever you use someone else’s idea.

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These webpages explain what referencing is, why it is important and give an overview of the main elements of how to reference. Our Referencing made simple tutorial opens in a new window and covers how to identify your source and create a reference with interactive examples.

Why reference?

Referencing correctly:

helps you to avoid plagiarism by making it clear which ideas are your own and which are someone else’s
shows your understanding of the topic
gives supporting evidence for your ideas, arguments and opinions
allows others to identify the sources you have used.

When to reference

Whenever you use an idea from someone else's work, for example from a journal article, textbook or website, you should cite the original author to make it clear where that idea came from. This is the case regardless of whether you have paraphrased, summarised or directly quoted their work. This is a key part of good practice in academic writing.

University and school policies

The University referencing policy (PDF) sets out the referencing requirements that all taught students and tutors are expected to follow.

Each school in the University requires students to use a specific style of referencing. Check the referencing style used in your school before you begin.

All your citations and references should match the style you are using exactly, including any punctuation, capitalisation, italics and bold, and you should use the same referencing style throughout your assignment.

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The art of referencing: Well begun is half done!

Department of Pediatrics, College of Medicine and Health Sciences, National University of Science and Technology, Sohar, Sultanate of Oman

Department of Pediatrics, Seth G.S. Medical College and K.E.M. Hospital, Mumbai, Maharashtra, India

Introduction

The value of scientific research lies in its wide visibility and access/availability to others; this is generally achieved by a scientific publication as an original (research) paper. The scientific inquiry typically advances based on previously laid ideas/research, making it essential to acknowledge the contribution of the previous authors. The references list is a catalog of literature sources chosen by the researcher to represent the most relevant documents pertaining to his/her study.[ 1 ] The British Standards Institution defines reference as “a set of data describing a document, sufficiently precise and detailed to identify it and enable it to be located.” [ 2 ] References lay the foundation of the paper, providing context for the hypothesis, methodology, interpretation, and justification of the study.[ 3 ] Using other's ideas/thoughts without due credit amounts to plagiarism, compromising the academic integrity of research. A well-referenced paper is thus accurate and complete, adds value and credibility to both the researcher and the source author, and enhances the scientific prestige of the chosen journal.[ 3 ] A bibliography also lists the sources used during research. However, while references only include those sources (journals, books, web information, etc.) which are actually cited in the publication, bibliography comprises all accessed sources (works consulted), irrespective of whether they are cited in the study publication or not.[ 4 ] Thus, referencing in academic writing is an important research tool to display as well as integrate knowledge on a particular subject or topic.[ 5 ]

Importance of Proper Referencing

Scientific research is usually developed on previously established ideas/scientific knowledge. A meticulous literature review at the beginning of the study enables the researcher to identify the work done in the field, identify the gaps in knowledge, and recognize the need for further research.[ 6 ] The most relevant sources from this literature search (essentially) form the list of references. Use of proper referencing is thus beneficial in many ways, such as the following:

a) It helps the readers to identify and locate the sources used in the research and provides evidence to verify the need/rationale of the study, methodology, inferences, and implications of the study.[ 3 ]
b) It provides an overview of the techniques/tools used, supports/convinces the reader about the appropriateness of the methodology, and offers a proper perspective in which the research findings need to be interpreted.[ 3 , 7 ]
c) It is a proof of the author's in-depth reading and knowledge on the subject pertaining to his/her research. References not only highlight similarities in research, but also differentiate the author's ideas from his sources, indirectly acknowledging the author's own contribution to that topic.[ 4 ]
d) References chosen by a researcher not only credit the individual author/s whose work is cited, but also demonstrate his/her appreciation toward cited authors, at times leading readers toward hitherto lesser-known/unknown author's research.[ 4 , 8 ] By providing acknowledgment to the cited idea/thought, the author also avoids being accused of plagiarism and adds credibility to his/her own work.[ 4 ]
e) Referenced works steer the readers toward literature pertaining to a particular topic, thus advancing the readers’ interest.[ 4 ] It also allows to trace the origins of ideas and integrates newer ideas (from current research) with previous ones, thus building a web of learning about the topic of interest.[ 9 ]
f) The reference list provides a list of experts in a specific field, thus helping editors to identify appropriate reviewers.[ 3 ]
g) It provides peer reviewers with related sources of information to evaluate the manuscript with respect to the cited work.[ 6 ]

Organizing the References

An initial extensive literature search helps in identifying the appropriate research question, drafting the study protocol, supervising ongoing research, analyzing the results, and writing the paper.[ 3 , 7 ] Although references are displayed at the end of the article/after the text of the article, they should not be actually written after completing the text of the manuscript. While drafting the text of the manuscript, the author/s should type the references on a separate MS Word document simultaneously. This preparation allows the writer to choose adequate number of relevant and rational references, avoid bias in his/her research/writing, and limit the reference number as per the target journal for publication.[ 7 ] While citing, it is imperative not to cite broadly, but to do so with respect to the content of the article. Articles which define the topic, lay down background information regarding the study question, give current knowledge about the research, and describe previous studies on a similar study question should be mentioned in the “Introduction” section of the manuscript.[ 10 ] These studies enable to identify existing knowledge, gaps in knowledge, and justify the rationale of the study.[ 6 ] Studies which identify or refer to the method, protocols, or standards (whether new or previously published), elaborate on complex or lesser-known statistical analysis, describe diagnostic criteria, rationalize sample size estimation, or justify use of specific study design/method are best suited as references to the “Methods” section of the manuscript – they help to plan a strong and supported methodology and describe the technique and criteria of the study group.[ 3 , 10 ] Research that reflects on the study findings/results or provides supportive explanation merit mention in the “Discussion” section of the manuscript – they provide information to interpret the study based on existing published data, compare results with those of other studies, and rationalize the implications of the results.[ 10 ]

Though citation analysis treats all references equally, it is important to weigh references in terms of their value to the paper.[ 11 ] While some references are worthy to be mentioned only once in the paper, some are very relevant to the study question and referred to on multiple occasions, and it is important to re-cite only the most relevant articles.[ 3 ] Referencing is not just about stating the publication source (providing relatedness), but also adds value to the paper in terms of representation on the subject and connectivity between knowledge sources (capture the “aboutness”).[ 11 ] References can be books (author/s), legal documents, journal articles, newspaper articles, reports (e.g., official reports from government departments), university working papers, papers presented at conferences, internet sources (including weblogs – blogs and email correspondence), DVD/CD databases, radio/television/videos/audio cassette/CD-ROMs, interview transcripts, and illustrations.[ 12 ]

Choosing Appropriate References

As a rule, whenever one uses an idea, data, diagrams, tables, concepts, methods from a previously published work, it should be cited.[ 12 ] With availability of multiple search engines and abundance of online resources, the task of filtering references may seem daunting.[ 5 ] While choosing references, one should ensure that the original source is completely read and correctly interpreted before its citing.[ 6 ] It is preferable to provide direct references to original article sources as far as possible, choosing a landmark article on the topic.[ 5 ] The choice of references should serve as the most relevant, appropriate, and valuable addition, and one should stick to the most pertinent references that actively support/contradict their conclusions or experience.[ 6 ] It is preferable to use the most recent relevant resources to provide the latest and up-to-date information; however, certain landmark papers may also be cited (even if they are old). Note that very old references may not be available/accessible to reviewers as well as readers.[ 7 ] Often, there are multiple sources for the same information; always prefer references that provide the highest level of evidence (such as meta-analysis), most recent publications, or trustworthy sources such as reputed peer-reviewed journals (with higher impact factor), open access and preferably indexed on reputed databases such as MEDLINE and PubMed.[ 13 , 14 ] Citing works from the journal one wishes to submit demonstrates that author follows that particular journal's publications and values it; however, one should refrain from unethical practices such as coercive citation (when authors are coerced/directed to add irrelevant citations from the editor's journals) or padded citation (when authors pad their reference list with superfluous citations).[ 14 , 15 , 16 ] There should be a judicious combination of original as well as review articles. Review articles summarize a large body of literature and reduce the number of references; however they may be biased and may not reflect the original article accurately.[ 16 ] One should stick to the journal guidelines rigorously (in terms of style and number) to avoid rejection or delay in the processing of the manuscript.[ 6 ] Avoid citing conference abstracts as far as possible, as they provide incomplete or limited information on the subject and often lack an appropriate peer review.[ 16 ] Other sources which lack traditional review and thus may cite inappropriate, unchecked, or promotional content include online sources, such as audio and video presentations, and should therefore be used with caution.[ 17 ] It is also prudent to avoid personal communications and limit their use to situations where essential information is unavailable from a public source (if permission is necessary, then name and date of the communication should be cited in brackets in text).[ 16 ] Limit self-citations to the bare crucial ones that are necessary.[ 18 ] Articles accepted but awaiting publications should be cited as “in press.”[ 16 ] Articles submitted but not yet published should be referenced as “unpublished observations” with written permission from the source; however, since they have not undergone a peer review, they should be (preferably) avoided.[ 16 ] It is prudent to avoid citing articles published in predatory journals.[ 16 ]

There is no need to provide references to facts that are expected to be well known to the journal readers, including historical overviews, own experiences, while outlining previously referenced ideas in conclusions, or while summarizing what is regarded as “common knowledge.”[ 12 ] One should be careful with online sources. There may be errors while copying the uniform resource locator (URL) or the webpage, or the website may change or be closed/inaccessible; hence, cite them only if very essential and check for their reliability and give the date of access.[ 3 ] It is preferable to use online sources with digital object identifiers (DOIs), assuring their permanent presence.[ 13 ] Also, before submission, it is worthwhile to check the US National Library of Medicine's (NLM's) PubMed database ( http://www.pubmed.org ) for any recently published articles related to the manuscript's topic.[ 19 ]

The number of references is determined by the target journal requirements as well as the type of manuscript submitted; for example, the Journal of Postgraduate Medicine allows about 30 references for original articles, up to 15 references for brief reports/grand rounds/clinicopathological forum, 12 references for case series, up to 10 references for case reports/research letter, and five references for a letter to editor ( https://www.jpgmonline.com/contributors.asp#Ref ).

Preparing the References

Citation consists of two components – the “in-text citation” and the “reference list.”[ 7 ] In the in-text citation, quotation marks are used to cite an exact line/phrase from another source, specifically for definitions, examples, or explanations provided by another/earlier author/s.[ 13 ] To prevent plagiarism, it is suitable to interpret and then summarize the cited content in one's own words, referencing the source at the end of the sentence.[ 14 ]

The parts and order in the citation depend on the source which the author is referencing (journal, book, book chapter, or web source) and the journal guidelines. It is imperative to go through the target journal rules and follow the “Instructions to Authors” related to referencing guidelines (the style, punctuation, italics, abbreviations, issue number, volume number, and pages). All the references are generally cited and numbered as per the order in which they are mentioned in the text (and are to be inserted immediately after the source information and not necessarily at the end of the sentence, especially when multiple facts are stated in a single sentence).[ 6 ] In case of a table or a figure, the citation number should be in sequence to that of the preceding text.[ 7 ] The same reference number in which the source is first cited should be used throughout the manuscript (if cited again) as well as in the reference list.[ 7 ] The citation numbers are placed as superscript/in parentheses as per the journal guidelines.[ 7 ] In case of multiple citations, place them immediately after the fact; they should be placed in order of their chronology of publication (or alphabetically if published in the same year) separated by commas.[ 6 , 7 ] If many references are cited consecutively, the numbers can be separated by a hyphen.[ 7 ]

Any documented knowledge (text, audio, or visual) can serve as a source of reference. They can be print based or electronic and include journals, books, doctoral theses, conference papers, newspapers and magazines, web pages, and so on.[ 4 ]

The basic elements while referencing are as follows:[ 13 , 20 ]

Journal/research paper: Name of author/s, title of paper, journal title (often abbreviated according to the style used for MEDLINE [ www.ncbi.nlm.nih.gov/nlmcatalog/journals ]),[ 16 ] publication year, volume number, issue number (issue number is kept optional by many journals), and page numbers (starting and ending page numbers or e-article number if the journal does not allot page numbers but allots e-article numbers only)[ 13 ]
Book/chapter: Chapter author/s, title of chapter, editor/s, name of book, edition, publisher, city of publication, year of publication, and page numbers[ 13 ]
Web sources: Names of author/s, title of webpage, year, weblink, date of access, and other information such as publisher, year of publication, and date of recent update (as may be applicable/available).[ 13 ] When citing a webpage, provide the DOI or URL of the original source as far as possible.[ 1 , 20 ]

Special attention needs to be paid to the punctuations while composing the reference, and the authors must adhere to the style recommended by the journal (that the manuscript will be eventually submitted to). Note that with each revision that the author makes in the manuscript, there may be changes in the order, addition, or deletion of references, and these adjustments should be meticulously ensured to avoid referencing errors.[ 3 ] It is also the author's responsibility to ensure that every citation has a corresponding reference and every reference is cited in the right place and context in the manuscript.[ 6 ] To avoid citation errors, the authors must verify each reference against an electronic bibliographic source like PubMed or print/pdf copies of original resources.[ 16 ] Authors should also verify that none of the cited references is a retracted article; this can be done via MEDLINE by searching PubMed for “Retracted publication [publication type]” or by going directly to the PubMed's list of retracted publications ( https://www.ncbi.nlm.nih.gov/pubmed/?termretractedpublication[publication type] ).[ 16 ]

“Recommendations for the Conduct, Reporting, Editing, and Publication of Scholarly Work in Medical Journals” issued by the International Committee of Medical Journal Editors (ICMJE) provides specific information on how to cite sources, which should be followed.[ 16 ] These recommendations by the ICMJE summarize and provide regular updates on how to cite various sources (print documents; unpublished material; audio and visual media; material on CD-ROM, DVD, or disk; and material on the Internet) via Sample References ( www.nlm.nih.gov/bsd/uniform_requirements.html ) on their webpage.[ 16 ] Detailed information is also available in the NLM's Citing Medicine, 2 nd edition ( www.ncbi.nlm.nih.gov/books/NBK7256/ ).[ 20 ] Number of references to be cited should be in accordance with/within the limits as stated in the “Author Guidelines” issued by the target journal.[ 7 ] Authors should take precaution, so as to avoid citing the same reference twice in the list of references.

Types of Referencing Formats/Styles

“Citation style” is the standard format in which the source is documented in the text as well as in the reference list at the end of the manuscript.[ 4 ] In-text citation styles can be broadly classified into numerical referencing style (Numeric style/Vancouver/Institute of Electrical and Electronic Engineers [IEEE] and Running notes style/Modern Humanities Research Association [MHRA]) and name referencing style (Author Date/Harvard, American Psychological Association [APA] and Modern Languages Association [MLA]).[ 12 ] The two major used citation styles are the Vancouver and the Harvard styles, and most other styles are minor modifications of these two styles.[ 4 ] The common citation styles and their examples are summarized in Table 1 .[ 3 , 12 , 13 , 16 , 20 ] Thus, there is a wide variability in the citation style in text as well as reference list; however, the author does not have a choice, but to stick to the style recommended by the journal to which he/she wishes to submit his/her research.[ 3 ]

Citation styles with examples[ 3 , 12 , 13 , 16 , 20 ]

Style	Example	Citation in reference list	Citation in main text
Vancouver “Citation sequence” format Common in journals of medical and physical sciences Used by PubMed and MEDLINE	Cines DB, Bussel JB. SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia. N Engl J Med 2021;384 (23):2254-2256.	In Arabic numerals as per chronological appearance in the main text	Within text/at the end of sentence Superscript or in parentheses i.e. (brackets); e.g., (Cines and Bussel, 2021)
Harvard “Author-date” style Common in humanities and social sciences Recognizes individual scientist’s contribution within text citation	Cines, D. B. and Bussel, J. B. (2021) SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia. , 384 (23), pp. 2254-2256.	Arranged alphabetically as per the surname of the authors	Surname of the author and year of publication in parentheses (brackets) (e.g., Cines and Bussel, 2021)
American Medical Association	Cines DB, Bussel JB. SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia. 2021;384 (23):2254-2256.	As per chronological appearance in the main text	Numerical in-text citations, written in superscript
American Psychological Association 7 edition Common in psychology and health sciences Similar to the Harvard style, differences being in citation punctuation, citing multiple authors, and referencing electronic sources	Cines, D. B., and Bussel, J. B. (2021). SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia. , 384 (23), 2254-2256.	Arranged alphabetically (author name and initials followed by the year of publication)	Surname of the author and year of publication in parentheses i.e. (brackets); e.g., (Cines and Bussel, 2021)
Modern Language Association 9 edition “Author-page” format Common in business and management studies, health education, humanities, sciences, computing and information technology, and in languages journals	Cines, Douglas B., and James B. Bussel. “SARS-CoV-2 Vaccine-Induced Immune Thrombotic Thrombocytopenia.” New England Journal of Medicine, vol. 384, no. 23, 2021, pp. 2254-56.	Arranged alphabetically (for the first author, surname comes first, followed by first names first for additional authors)	Author’s surname and a page number (e.g., Cines and Bussel 2254-56)
National Library of Medicine	Cines DB, Bussel JB. SARS-CoV-2 vaccine-induced immune thrombotic thrombocytopenia. N Engl J Med 2021 June 10;384 (23):2254-6.	As per chronological appearance in the main text	There is flexibility to cite from the following three styles: 1. Author-Year system 2. Sequence system 3. Author-sequence system

Common Errors in Referencing

Referencing is a tedious task and if not taken seriously and performed diligently, it is prone to many (easily avoidable) errors.[ 7 ] A reference should be accurate, clear, and consistent throughout the manuscript.[ 6 ] An incorrect reference not only questions the credibility of the paper, but also makes it difficult for the reviewers and the readers to seek the cited article, thus denying the source author of due credit for his/her work.[ 3 ] It is the author's responsibility to cite the most relevant and appropriate references in his/her research.[ 3 ] The author should not only locate, read, and understand all sources cited by him/her ( intellectual pleasure ), but also confirm the source and provide all elements of the source correctly ( accuracy ).[ 6 ] The author should be careful not to copy references from an earlier article, but should actually rewrite each selected reference afresh.[ 6 ] Some common errors occurring during referencing are summarized in Table 2 .[ 6 , 7 ]

Common errors in the “in-text citation” and the “reference list”[ 6 , 7 ]

Errors in citation	Errors in reference list
Citing a cross reference without reading the original source	The journal format is not followed/not adhered to
Duplication of citation in the manuscript	Reference is just copied from another published article without verifying the original source reference
In-text citation does not adhere to the format of the target journal	Errors in listing names of authors, journal, year, volume number, page numbers, and so on
Multiple citations put at the end of the sentence instead of mentioning the reference just after the fact that the particular reference specifically pertains to	Error in number of authors listed
In-text citation without mentioning the reference in the reference list	Incorporating irrelevant information such as issue number, date and month of publication (when the target journal does not need it, as per the journal’s instructions to authors)
Citing a reference based on its abstract only (and without reading the full paper)	Resubmitting a rejected article to another journal without modifying in-text citation or reference list as per the new journal’s requirements
Using personal communications as references Referencing the abstract and results sections of the manuscript	Citing the print version of a source while the online version has been accessed Citing retracted references

Reference Management Software

As described earlier, there is a wide variation in the journal formatting styles and it is laborious for the researcher to store, organize, and manage the references throughout the process of literature review and protocol planning till the drafting and manuscript submission.[ 21 ] Even more challenging is the addition/deletion or reordering of references (in text as well as in the reference list) with each revision or submission to a newer journal.[ 22 ] There is an increased likelihood of making errors in citing, especially while organizing the references and writing the reference list.[ 23 ] To minimize such errors, reference management software (RMS), also known as citation management software or bibliographic management software, are available to the authors/researchers.[ 21 ] They not only help to search and retrieve the online scientific sources, but also help to import them to their database for storing, organization, and subsequent retrieval.[ 22 ] Many RMS have cloud-based storage, enabling users to be able to access the information from multiple devices as well as collaborate with other researchers.[ 22 ] RMS also allow authors to retrieve citations while writing in the format of desired journal, thus permitting to “cite while you write.”[ 14 ] They also enable addition, deletion, insertion of references in the text and automatic (auto) resequencing of their order in the main manuscript (text) as well as in the reference list.[ 22 ] They can generate reference lists in multiple formats/citation styles to suit the target journal requirements and allow conversion of one format style to another with ease at the click of the mouse.[ 14 ] By linking each citation with a full reference, they ensure each citation in the text is accounted for by a corresponding full reference in the list.[ 12 ] Most of them are compatible for use with common programs such as Microsoft Word and Google Docs.[ 24 ]

There are numerous programs for reference management available in the market – independent applications, those operating within an internet interface, and combination of both these modes.[ 1 ] The most commonly used are Mendeley by Elsevier ( www.mendeley.com ), EndNote ( www.endnote.com ) by Thomson Reuters, and Zotero ( www.zotero.org ).[ 1 ] Some others are RefWorks, F1000 Workspace, JabRef, Citavi, Bibsonomy, ReadCube Papers, Colwiz, Sente, RefME, Connotea, CiteULike, BibTeX, and Microsoft Word.[ 22 , 24 , 25 ] While many of them are free, some are fee based and require a (paid) subscription.[ 13 ]

Despite the use of RMS, one cannot guarantee absence of referencing errors, as there can be errors in details (author names, journal title, dates) or duplication of references when retrieved from different databases.[ 23 ] So, ultimately, the authors (themselves) are responsible for the accuracy of the references cited by them (whether they do the referencing using RMS or manually).

Thus, referencing is an essential part of research and should be assigned due importance, right from the conception of the study question till its delivery as a publication. It plays a vital role throughout the manuscript and appears in almost all sections – from laying down the foundation for study rationale (in the “Introduction” section of the manuscript), describing/justifying the study procedure/s (in the “Methods” section), validating the results (in the “Results” section) and its implications (in the “Discussion” section of the manuscript). References are also utilized by editors to identify subject experts for peer review, by readers to obtain more resources on the subject matter, and by peer reviewers to critically evaluate the manuscript in the light of the available evidence. It is thus essential that references are chosen wisely and carefully as they are representative of the study. It is the author's responsibility to confirm the clarity, accuracy, and appropriateness of the cited sources. One should be careful to avoid common referencing errors to prevent delay/rejection by the journal of interest. As Vancouver style is the commonly preferred citation style by journals of medicine and health sciences, researchers should be well versed with it. Authors should diligently stick to the instructions and style of the target journal. The availability of reference management software such as Mendeley and EndNote has made the authors’ task of collecting, storing, organizing, retrieving, and utilizing the references more efficient and easier; however, it is still the authors’ responsibility to select appropriate references and cite them accurately and correctly.

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Academic and Writing Resources

Writing Research Papers

What Types of References Are Appropriate?

When writing a research paper, there are many different types of sources that you might consider citing. Which are appropriate? Which are less appropriate? Here we discuss the different types of sources that you may wish to use when working on a research paper.

Please note that the following represents a general set of recommended guidelines that is not specific to any class and does not represent department policy. The types of allowable sources may vary by course and instructor.

Highly appropriate: peer-reviewed journal articles

In general, you should primarily cite peer-reviewed journal articles in your research papers. Peer-reviewed journal articles are research papers that have been accepted for publication after having undergone a rigorous editorial review process. During that review process, the article was carefully evaluated by at least one journal editor and a group of reviewers (usually scientists that are experts in the field or topic under investigation). Often the article underwent revisions before it was judged to be satisfactory for publication.

Most articles submitted to high quality journals are not accepted for publication. As such, research that is successfully published in a respected peer-reviewed journal is generally regarded as higher quality than research that is not published or is published elsewhere, such as in a book, magazine, or on a website. However, just because a study was published in a peer-reviewed journal does not mean that it is free from error or that its conclusions are correct. Accordingly, it is important to critically read and carefully evaluate all sources, including peer-reviewed journal articles.

Tips for finding and using peer-reviewed journal articles:

Many databases, such as PsycINFO, can be set to only search for peer-reviewed journal articles. Other search engines, such as Google Scholar, typically include both peer-reviewed and not peer-reviewed articles in search results, and thus should be used with greater caution.
Even though a peer-reviewed journal article is, by definition, a source that has been carefully vetted through an editorial process, it should still be critically evaluated by the reader.

Potentially appropriate: books, encyclopedias, and other scholarly works

Another potential source that you might use when writing a research paper is a book, encyclopedia, or an official online source (such as demographic data drawn from a government website). When relying on such sources, it is important to carefully consider its accuracy and trustworthiness. For example, books vary in quality; most have not undergone any form of review process other than basic copyediting. In many cases, a book’s content is little more than the author’s informed or uninformed opinion.

However, there are books that have been edited prior to publication, as is the case with many reputable encyclopedias; also, many books from academic publishers are comprised of multiple chapters, each written by one or more researchers, with the entire volume carefully reviewed by one or more editors. In those cases, the book has undergone a form of peer review, albeit often not as rigorous as that for a peer-reviewed journal article.

Tips for using books, encyclopedias, and other scholarly works:

When using books, encyclopedias, and other scholarly works (that is, works written or produced by researchers, official agencies, or corporations), it is important to very carefully evaluate the quality of that source.
If the source is an edited volume (in which case in the editor(s) will be listed on the cover), is published by a reputable source (such as Academic Press, MIT Press, and others), or is written by a major expert in the field (such as a researcher with a track record of peer-reviewed journal articles on the subject), then it is more likely to be trustworthy.
For online encyclopedias such as Wikipedia, an instructor may or may not consider that an acceptable source (by default, don’t assume that a non-peer reviewed source will be considered acceptable). It is best to ask the instructor for clarification. 1

Usually inappropriate: magazines, blogs, and websites

Most research papers can be written using only peer-reviewed journal articles as sources. However, for many topics it is possible to find a plethora of sources that have not been peer-reviewed but also discuss the topic. These may include articles in popular magazines or postings in blogs, forums, and other websites. In general, although these sources may be well-written and easy to understand, their scientific value is often not as high as that of peer-reviewed articles. Exceptions include some magazine and newspaper articles that might be cited in a research paper to make a point about public awareness of a given topic, to illustrate beliefs and attitudes about a given topic among journalists, or to refer to a news event that is relevant to a given topic.

Tips for using magazines, blogs, and websites:

Avoid such references if possible. You should primarily focus on peer-reviewed journal articles as sources for your research paper. High quality research papers typically do not rely on non-academic and not peer-reviewed sources.
Refer to non-academic, not peer-reviewed sources sparingly, and if you do, be sure to carefully evaluate the accuracy and scientific merit of the source.

Downloadable Resources

How to Write APA Style Research Papers (a comprehensive guide) [ PDF ]
Tips for Writing APA Style Research Papers (a brief summary) [ PDF ]

Further Resources

How-To Videos

Writing Research Paper Videos

Databases and Search Engines (may require connection to UCSD network)

Google Scholar
PubMed (NIH/NLM)
Web of Science

UCSD Resources on Finding and Evaluating Sources

UCSD Library Databases A-Z
UCSD Library Psychology Research Guide: Start Page
UCSD Library Psychology Research Guide : Finding Articles
UCSD Library Psychology Research Guide : Evaluating Sources

External Resources

Critically Reading Journal Articles from PSU/ Colby College
How to Seriously Read a Journal Article from Science Magazine
How to Read Journal Articles from Harvard University
How to Read a Scientific Paper Infographic from Elsevier Publishing
Tips for searching PsycINFO from UC Berkeley Library
Tips for using PsycINFO effectively from the APA Student Science Council

1 Wikipedia articles vary in quality; the site has a peer review system and the very best articles ( Featured Articles ), which go through a multi-stage review process, rival those in traditional encyclopedias and are considered the highest quality articles on the site.

Prepared by s. c. pan for ucsd psychology, graphic adapted from t-x-generic-apply.svg , a public domain creation by the tango desktop project..

Research Paper Structure
Formatting Research Papers
Using Databases and Finding References
Evaluating References and Taking Notes
Citing References
Writing a Literature Review
Writing Process and Revising
Improving Scientific Writing
Academic Integrity and Avoiding Plagiarism
Writing Research Papers Videos

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How Many References in a Research Paper?

Junior researchers frequently wonder how many references should be included in their research papers. The common response? “As many as you need.” What exactly does that mean? While we admit there are very few hard-set rules regarding this issue, in this article, we will try to provide more concrete guidelines that will help you assess whether you have enough references in your paper.

Before we do so, let us briefly explain why references matter and whether the number of references you include can project certain perceptions about the quality of your work. There is such a thing as having too many or too few.

Why are research paper references and citations necessary?

References show that you have carefully reviewed the relevant literature and are now contributing something novel to the academic community. You establish authority and credibility when you can critically assess other literature and distinguish your findings from previous works (if any exist). We emphasize “critically assess” in the last sentence because references are only as good as you apply them to your research. Therefore, the famous adage “quality over quantity” is the key to deciding how many references are sufficient.

Likewise, citing your references within the research paper itself (in the form of academic citations ) is crucial in any academic work that makes assertations based on external studies. Failing to cite your sources can result in plagiarism, which even if accidental can still have some devastating consequences for academic researchers hoping to publish their work or finish graduate school.

Number of Sources Used Can Impact Perceptions of Quality

We would be remiss if we didn’t tell you that being at either extreme (having too few or too many references) can reflect poorly on your intellectual aptitude and your study’s validity. Here’s why:

If you don’t have enough references, particularly on a topic familiar to a wide audience, readers may think that you haven’t done enough research into existing literature. Surely someone else has thought about related topics or used similar techniques. If you’re sloppy in conducting your diligence, readers will wonder whether your paper is worth reading. What’s novel and valuable about your paper? Were you just as sloppy with conducting your study? The answers to these questions need to be evident.
Additionally, readers might be concerned that you may have plagiarized by failing to properly cite information. Unless you’re John Nash, who cited only two texts in his seminal 26-page PhD thesis (one of which was to his prior work), ensure that you’ve properly researched the relevant papers and included appropriate citations! Especially, make sure that you have found, read, and included all the latest publications on your topic before finalizing and submitting your own paper—if the drafting process took some time, new literature might have come out in the meantime, and you don’t want to give the editor the impression that you are not on top of the newest developments.
If you have too many references, readers may wonder if you did any original research at all. Unless you’re writing a literature review, your paper’s primary focus should be on your investigation and findings. Don’t bury your hard work under strings of citations and discussion regarding other works. Show your readers what you’ve discovered and how the new information you present fits into or departs from the academic community’s current understanding of your topic.

Additionally, let us highlight the difference between the number of references versus citations. References are the source materials; therefore, each reference should be listed only once in your references section. Citations are meant to identify the source of the information you use in your paper. You can cite a reference multiple times. Therefore, the number of citations you have is typically larger than the number of references an average paper includes. The opposite situation should never happen!

Key Factors Influencing the Number of References You Use

The following are some of the many factors that may influence the number of references you use:

The number of references required for a paper will depend largely on your work’s purpose . For example, literature and systematic reviews are surveys of existing studies. Therefore, their reference lists will be more exhaustive than those of research papers whose primary focus is the current authors’ findings. Indeed, if you examine many journals’ author guidelines , you’ll note that journals have a higher maximum reference limit for review articles than original research papers.
The length of your reference list will also depend on your research paper’s subject matter . For example, if you are writing about a field that is less studied (such as a subfield of neuroparasitology) you may discover that there aren’t many papers to cite. Similarly, newer fields will have fewer published papers that can be referenced. If you find yourself in this situation, review the references used by relevant current literature and see if you can expand your research, and thus your reference list, with valuable content from there.
Another factor will be your institution or journal’s requirements . If you are preparing a dissertation or thesis, double-check your department’s requirements. While rare, they may have specific limits. More commonly, journals restrict the number of references due to printing constraints.
It may happen that you don’t have access to certain literature that could have served as a reference. In such a situation, you may wish to look for an institution that may be able to provide you access to that literature for the purposes of reviewing the content or contact one of the authors directly and ask for a copy.
Given that more papers are being published than ever before in most fields, it is likely that reference lists will grow longer simply because there are more data and discussions of existing data available to cite . Keep track of changes to the size of reference lists in publications related to your field.
Finally, a paper’s length bears some correlation to the number of references.

So how many references should be included?

Below, we provide tips on how to decide if you have enough resources. We also provide some general reminders on how to effectively use references. After all, references are meant to enhance your paper while still maintaining your research as the focal point.

Use academic journals as a guide

One way to gauge how many references you should have is to survey academic journals for your article type in your field. Review their author guidelines for limits on the number of references for your article type, and make sure your reference list complies with those journal restrictions.
Read recent articles relevant to your topic; check how many references other authors have included in their papers for the same article type as yours, and how frequently those works were cited per page.
Keep in mind that the above methods will give you an estimate of how many references you should include overall but will not tell you how many citations you’ll need per page. The latter is impossible to state simply because certain sections may have no citations at all (the results section , for example).

Statistics regarding the number of references and citations

To give you a general idea, the following are some estimates from a couple of studies that examined the citation characteristics of articles published in various disciplines.

According to Milojević’s study encompassing research in the fields of astronomy, mathematics, robotics, ecology, and economics, the highest and average number of references per article page were as follows:

Ecology: highest, ~58; average reference per page, 6;
Math and robotics: highest, ~28; average reference per page, <1; and
Economics: highest, ~ 32; average reference per page, >1 but <2.

The above findings were based on data compiled from the first 20 years of the author’s research. Since then some fields have increased the number of references. Thus, make sure to examine your target journal’s most recent and relevant publications for a better idea of how many references to include based on the specific type of article you plan to write.

In another study by Falagas et al. (2013), medical journals averaged 29 references for articles that were 7.88 pages long (as printed in journals).

Finally, although the sample size was small (63 journals), Gali Halevi observed the following citation trends of a broader range of disciplines.

The average number of references per article was the highest for the social sciences, physics, and astronomy, and arts & humanities (roughly 54 references per article).
On the other hand, health professions and earth and planetary sciences had the fewest references per article at an average of 8 and 17 references, respectively.
Math and engineering averaged at roughly 29 references per article.
Biochemistry, genetics and molecular and other biological sciences averaged at 51.
Hard and natural sciences more frequently cited recent literature while social sciences and math were likely to include older sources.

Note that the Halevi study is limited in size, fails to factor in article type and does little to account for variances across different fields and journals. For example, it is possible that more review articles could have been reviewed for certain fields than others. With that said, we provide the above information to provide a rough estimate.

At the end of the day, please keep in mind the requirements of your institution or target journal and the general trends for your specific article type (by examining the most recent relevant publications).

For additional information regarding journal restrictions on the number of references, read this article on ways to grow your publication list .

Some Dos and Don’ts for Reference Citation

Don’t repeat references within a reference list.
Don’t repeatedly cite yourself. Make sure to balance your discussion with external literature citations.
Be careful about citing old references. The rule of thumb is to go back at most five to six years. Exceptions to this rule should be reserved for “seminal” works relevant to explaining what prompted your research. Roughly 85% of all cited works should be less than five years old.
Be careful not to cite several references in one place without discussing the relevance of each work to your research. In other words, don’t say, “We referred to previous studies in this field (1-7)” unless you later explain how each of reference #s 1-7 apply to your discussion.
Confirm the quality of the work you cite. Are there any ethical issues regarding the paper that would disqualify it as a good source? Do your references come from reputable sources such as respected journals rather than random blogs and website links? Remember that your analysis is only as good as the verifiable information you use to conduct your research.
One of the main purposes of citing existing literature is to show the “knowledge gap” regarding your topic. Therefore, make sure the works you reference naturally lead readers to wonder about the research question you address in your paper. To explain further, think about your favorite fictional story. A successfully written story only reveals the background information needed for the reader to follow along in the story. You’ll rarely see an author waste time writing about how the main character stubbed his toe one day while going to work unless that event relates to an important aspect of the story. Similarly, the references you cite should support the story building you create in your research paper.
Don’t completely ignore the paper that could disprove your hypothesis. You want to show objectivity and that you took a balanced and unbiased approach to conducting your research. Mention the potentially conflicting evidence and explain why you believe it is flawed or inapplicable to your research.
In qualitative research papers, you may have fewer references.
Anything you cite in your paper should be listed in the references section (or reference list). Anything listed as a reference should have been quoted or paraphrased in the text. If either rule is violated, something is wrong.
Finally, remember that a paper will typically have more citations in the Introduction section and Discussion section than in other parts.

Wordvice Academic Resources

If you need help with paraphrasing text from the sources you cite to avoid plagiarism, with different citation styles , or with finding the perfect journal to submit your paper to, then have a look at our collection of articles on the Wordvice academic resources website . We also recommend our professional English editing and proofreading services , including paper editing and academic editing services to ensure that your writing is free of errors before submitting your manuscript to a journal.

How to cite ChatGPT

Use discount code STYLEBLOG15 for 15% off APA Style print products with free shipping in the United States.

We, the APA Style team, are not robots. We can all pass a CAPTCHA test , and we know our roles in a Turing test . And, like so many nonrobot human beings this year, we’ve spent a fair amount of time reading, learning, and thinking about issues related to large language models, artificial intelligence (AI), AI-generated text, and specifically ChatGPT . We’ve also been gathering opinions and feedback about the use and citation of ChatGPT. Thank you to everyone who has contributed and shared ideas, opinions, research, and feedback.

In this post, I discuss situations where students and researchers use ChatGPT to create text and to facilitate their research, not to write the full text of their paper or manuscript. We know instructors have differing opinions about how or even whether students should use ChatGPT, and we’ll be continuing to collect feedback about instructor and student questions. As always, defer to instructor guidelines when writing student papers. For more about guidelines and policies about student and author use of ChatGPT, see the last section of this post.

Quoting or reproducing the text created by ChatGPT in your paper

If you’ve used ChatGPT or other AI tools in your research, describe how you used the tool in your Method section or in a comparable section of your paper. For literature reviews or other types of essays or response or reaction papers, you might describe how you used the tool in your introduction. In your text, provide the prompt you used and then any portion of the relevant text that was generated in response.

Unfortunately, the results of a ChatGPT “chat” are not retrievable by other readers, and although nonretrievable data or quotations in APA Style papers are usually cited as personal communications , with ChatGPT-generated text there is no person communicating. Quoting ChatGPT’s text from a chat session is therefore more like sharing an algorithm’s output; thus, credit the author of the algorithm with a reference list entry and the corresponding in-text citation.

When prompted with “Is the left brain right brain divide real or a metaphor?” the ChatGPT-generated text indicated that although the two brain hemispheres are somewhat specialized, “the notation that people can be characterized as ‘left-brained’ or ‘right-brained’ is considered to be an oversimplification and a popular myth” (OpenAI, 2023).

OpenAI. (2023). ChatGPT (Mar 14 version) [Large language model]. https://chat.openai.com/chat

You may also put the full text of long responses from ChatGPT in an appendix of your paper or in online supplemental materials, so readers have access to the exact text that was generated. It is particularly important to document the exact text created because ChatGPT will generate a unique response in each chat session, even if given the same prompt. If you create appendices or supplemental materials, remember that each should be called out at least once in the body of your APA Style paper.

When given a follow-up prompt of “What is a more accurate representation?” the ChatGPT-generated text indicated that “different brain regions work together to support various cognitive processes” and “the functional specialization of different regions can change in response to experience and environmental factors” (OpenAI, 2023; see Appendix A for the full transcript).

Creating a reference to ChatGPT or other AI models and software

The in-text citations and references above are adapted from the reference template for software in Section 10.10 of the Publication Manual (American Psychological Association, 2020, Chapter 10). Although here we focus on ChatGPT, because these guidelines are based on the software template, they can be adapted to note the use of other large language models (e.g., Bard), algorithms, and similar software.

The reference and in-text citations for ChatGPT are formatted as follows:

Parenthetical citation: (OpenAI, 2023)
Narrative citation: OpenAI (2023)

Let’s break that reference down and look at the four elements (author, date, title, and source):

Author: The author of the model is OpenAI.

Date: The date is the year of the version you used. Following the template in Section 10.10, you need to include only the year, not the exact date. The version number provides the specific date information a reader might need.

Title: The name of the model is “ChatGPT,” so that serves as the title and is italicized in your reference, as shown in the template. Although OpenAI labels unique iterations (i.e., ChatGPT-3, ChatGPT-4), they are using “ChatGPT” as the general name of the model, with updates identified with version numbers.

The version number is included after the title in parentheses. The format for the version number in ChatGPT references includes the date because that is how OpenAI is labeling the versions. Different large language models or software might use different version numbering; use the version number in the format the author or publisher provides, which may be a numbering system (e.g., Version 2.0) or other methods.

Bracketed text is used in references for additional descriptions when they are needed to help a reader understand what’s being cited. References for a number of common sources, such as journal articles and books, do not include bracketed descriptions, but things outside of the typical peer-reviewed system often do. In the case of a reference for ChatGPT, provide the descriptor “Large language model” in square brackets. OpenAI describes ChatGPT-4 as a “large multimodal model,” so that description may be provided instead if you are using ChatGPT-4. Later versions and software or models from other companies may need different descriptions, based on how the publishers describe the model. The goal of the bracketed text is to briefly describe the kind of model to your reader.

Source: When the publisher name and the author name are the same, do not repeat the publisher name in the source element of the reference, and move directly to the URL. This is the case for ChatGPT. The URL for ChatGPT is https://chat.openai.com/chat . For other models or products for which you may create a reference, use the URL that links as directly as possible to the source (i.e., the page where you can access the model, not the publisher’s homepage).

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How can I tell if a paper is too old to be a reference for my research?

Current scientific databases hold papers that were published over the past few decades (I haven't checked what is the oldest paper available, but I remember seeing papers from the 1960s, there might even be older papers than that which are cataloged in current databases - not talking about the principia ...). One can come upon such old papers either when searching through a database or as a reference in a more recent paper.

My question is: how can I tell if a paper is too old such that I had better not rely on its findings while performing a more contemporary research?

(It probably differs between disciplines, so I'm looking for some general advice.)

publications
research-process

5 Student's classical paper is from 1908 - nothing is to old to cite if relevant. Cayley's paper from 1859 is still useful. Etc. etc. – user68958 Commented Jul 17, 2018 at 12:19
In my field, I still see people citing Gerhard Gentzen's paper on cut elimination occasionally! (FWIW that one's from the 1930s) – xuq01 Commented Jul 17, 2018 at 15:08
Look how many modern manuscripts cite Fick (1855) . Such old papers are fun to read and often appropriate in the introduction. Of course, often they don't need to be cited since they've become textbook knowledge. – user9482 Commented Jul 17, 2018 at 15:12
2 Yesterday I read a computer science paper whose oldest reference was from the 12th century. I regulary cite publications from the 18th and 19th centuries. – JeffE Commented Jul 19, 2018 at 13:54
1 @JeffE: Care to share what you were reading yesterday? – Mark Meckes Commented Jul 19, 2018 at 19:04

3 Answers 3

The age of the paper per se should have no relevance. However, the researcher had better be certain about whether the conclusions of the old paper have been superseded or even invalidated by more recent work. This sort of problem is unlikely in, say Mathematics, but other fields can be different. There are Philosophy papers that, to my knowledge, have invalidated old work. The old work said "X is impossible". The new work said "X is indeed possible and here is an important example." This wasn't mathematical philosophy (logic) of course, but observations about learning (epistemology).

The fact that a paper hasn't been cited in 50 years is of little importance, especially in a narrow subfield of some larger field. The fact that it is no longer relevant is of vast importance. However, there are some studies intentionally done to compare the old with the new and here, citing both is the essence, of course.

One reason for not finding old papers is just the difficulty and expense of properly indexing them in databases. For "popular" things someone is likely to want to go to the trouble, but for arcane things, not so much as there seems to be little payback for the effort.

And yes, you normally don't need to go back before the Principia, but, you know, Euclid was an interesting guy.

Note that another question here asks about finding more recent papers than the one you are reading.

Thanks, that question is one of mine as well... ;-) – Don_S Commented Jul 17, 2018 at 15:27

how can I tell if a paper is too old such that I had better not rely on its findings while performing a more contemporary research?

It may be a little difficult to give a general guideline. However, a few points may come in handy here.

If you look into most contemporary work, you could find some patterns in their references. In other words, may of them would have some very common papers which they cite. It is reasonable to know for what reasons these papers are cited by checking where in the text they are cited.
The references of this contemporary work may also have some old references cited for specific reasons, for this reasons you may also cite these references.
Citing very old references may be very beneficial if you are able to properly trace developments in the area over the years. However this may be a bit difficult as a lot of literature may have to be reviewed.
Another thing is that, sometimes, the author may come up with something absolutely novel which changes a fundamental notion or aspect from those "old references". Such papers will draw the attention of the research community to a completely different finding which may impact on the domain for years to come.

In summary, in my humble opinion, it is not easy to say that papers from a particular year becomes absolutely obsolete for research today. As a general rule, based on my experience, new researchers are usually encouraged to extend their research from a recent (say now till five years back) publication. However, for some of the reasons mentioned above, there are circumstances where new values may emerge from those very old research papers.

Mostly, the age of a publication should not be an argument against citing it, as mentioned by Buffy and Abdulhameed. I agree with their answers but I'd like to add that for certain statements about state-of-the-art or recent developements, you absolutely need up-to-date references.

An example for why this is necessary is that it would make no sense to cite a 20 year old paper to show how widely used a particular software is used, because the information from the paper is outdated. You could, however, look for more recent publications citing this paper. That way, you'd get better evidence for whatever it is you'd like to show.

You must log in to answer this question.

Not the answer you're looking for browse other questions tagged publications research-process reading ..

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COMMENTS

citations
24. I have read that references in scientific papers should be no more than 2-3 years old, since such fields move fast, and no more than 10 years for arts or related fields: A good rule of thumb is to use sources published in the past 10 years for research in the arts, humanities, literature, history, etc.
The "outdated sources" myth
What it means to be "timely" varies across fields or disciplines. Seminal research articles and/or foundational books can remain relevant for a long time and help establish the context for a given paper. For example, Albert Bandura's Bobo doll experiment (Bandura et al., 1961) is often cited in contemporary social and child psychology ...
How Old Should Your Article References Be? Based on 3,823,919 Examples
Note that the reference age is calculated by subtracting the publication year of the reference from that of the paper citing it. The table below shows that: The median reference cited in a research paper is 7-years-old, and 75% of references were published within the past 13-years. Still, 5% of papers cited sources older than 27 years, some ...
FAQ: How old should or can a source be for my research?
A good rule of thumb is to use sources published in the past 10 years for research in the arts, humanities, literature, history, etc. For faster-paced fields, sources published in the past 2-3 years is a good benchmark since these sources are more current and reflect the newest discoveries, theories, processes, or best practices. Use the ...
Cases when old references are valid?
5. It depends on the purpose of your reference. If you cite a paper to show the state-of-the-art, then older papers might be only acceptable for very niche fields, without too many publications. If you compare your results with an older paper, than you have to have a good explanation why such comparison is insightful.
Why you should use older references in your thesis
Why you should use older references in your thesis. May 10, 2016August 1, 2016 Graduate Research School (Auckland University of Technology) By Julia Hallas, PhD Candidate. "Never use references that are older than three years" was the advice given by a journal article reviewer I went along to hear recently. Yet a postgraduate supervisor who ...
How recent is recent for good referencing?
Cited articles (i.e., references) in a research paper play a central role in demonstrating the necessity of the research and establishing the validity and significance of the research results. ... All being said, do we exactly know how old a research article can be before it gets the label of not being recent i.e., an old article not good for ...
How Old Should References be: Best Age of Sources in writing
The best practice is that a reference should not be older than 5 years to ensure that the source is as recent as possible. However, when researching old topics like history and scientific data, your sources can be older since such content requires accuracy over recency. Regardless, the majority of sources should be within 5 years.
References: How to Cite and List Correctly
If a single reference points to more than one source, list the source numbers in a series, for example, as 1,3,6. Use a dash to separate more than two numbers as 1−3, if these form a sequence. However, use a comma to separate two numbers as 1,3 (without space in between), if these do not form a sequence.
Organizing Your Social Sciences Research Paper
A citation is a formal reference to a published or unpublished source that you consulted and obtained information from while writing your research paper. It refers to a source of information that supports a factual statement, proposition, argument, or assertion or any quoted text obtained from a book, article, web site, or any other type of ...
How Old Sources for References and Literature Review should be
The age of your references in a research paper should not be older than 5 years old unless otherwise stated. This applies where possible, as some papers require older sources. ... The content and context of the paper also determine how old the references should be. For example, imagine being given a topic concerning the economic impact of COVID ...
How to Cite Sources
A reference list (aka "Bibliography" or "Works Cited," depending on the style) is where you provide full information on each of the sources you've cited in the text. ... At college level, you must properly cite your sources in all essays, research papers, and other academic texts (except exams and in-class exercises). Add a citation ...
Ten simple rules for responsible referencing
What counts as proper citation practice in molecular biology—for instance, the inclusion of multiple references following a statement—is considered unacceptable in research ethics or science policy, in which single references require paragraphs of contextualisation and translation (see Rule 9). When reading a paper from an adjacent ...
The Importance of Proper Citation of References in Biomedical Articles
In medical science it can be customary to list references only from papers that are directly used (cited) in the text). During writing the author can read and study many articles, ... Research Methods of scientifically important publications include qualitative and quantitative methods and computer analysis approach (6, 8, 13). Garfield has ...
When is it appropriate to describe research as "recent"?
For example, if you cite sources from the current century as well as 1930s, then a paper from 2010 should be considered recent, but not one from 1950. If, on the other hand, your temporal range of references is rather narrow, say, recent 20 years, then you should refer to as "recent" for sources that are from approximately last 4-5 years.
Reference List: Basic Rules
Reference List: Basic Rules. This resourse, revised according to the 7 th edition APA Publication Manual, offers basic guidelines for formatting the reference list at the end of a standard APA research paper. Most sources follow fairly straightforward rules. However, because sources obtained from academic journals carry special weight in research writing, these sources are subject to special ...
When is the evidence too old?
A few weeks ago, when submitting an abstract to a nursing conference, I was suddenly faced with a dilemma about age. Not my own age, but the age of evidence I was using to support my work. One key element of the submission criteria was to provide five research citations to support the abstract, and all citations were to be less than ten years old.
Why and when to reference
Referencing is an important part of academic work. It puts your work in context, demonstrates the breadth and depth of your research, and acknowledges other people's work. You should reference whenever you use someone else's idea. View video using Microsoft Stream(link opens in a new window, available for University members only) These ...
PDF 7th edition Common Reference Examples Guide
More information on references and reference examples are in Chapters 9 and 10 of the Publication Manual as well as the Concise Guide to APA Style (7th ed.). Also see the Reference Examples pages on the APA Style website. Journal Article (Section 10.1)
How Are Academic Age, Productivity and Collaboration Related to Citing
For example, whether references are perfunctory or are essential to the paper , whether researchers cite to give credit or to persuade , whether references are given in positive or negative connotations , or even whether references can be a product of deliberate "gaming" of a system . Such micro-level behavior, although interesting, does ...
The art of referencing: Well begun is half done!
Organizing the References. An initial extensive literature search helps in identifying the appropriate research question, drafting the study protocol, supervising ongoing research, analyzing the results, and writing the paper.[3,7] Although references are displayed at the end of the article/after the text of the article, they should not be actually written after completing the text of the ...
What Types of References Are Appropriate?
Usually inappropriate: magazines, blogs, and websites. Most research papers can be written using only peer-reviewed journal articles as sources. However, for many topics it is possible to find a plethora of sources that have not been peer-reviewed but also discuss the topic.
How Many References in a Research Paper?
Math and engineering averaged at roughly 29 references per article. Biochemistry, genetics and molecular and other biological sciences averaged at 51. Hard and natural sciences more frequently cited recent literature while social sciences and math were likely to include older sources.
How to cite ChatGPT
The in-text citations and references above are adapted from the reference template for software in Section 10.10 of the Publication Manual (American Psychological Association, 2020, Chapter 10). Although here we focus on ChatGPT, because these guidelines are based on the software template, they can be adapted to note the use of other large ...
How can I tell if a paper is too old to be a reference for my research?
Current scientific databases hold papers that were published over the past few decades (I haven't checked what is the oldest paper available, but I remember seeing papers from the 1960s, there might even be older papers than that which are cataloged in current databases - not talking about the principia...).One can come upon such old papers either when searching through a database or as a ...
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