When to Cite.

Now that you have consulted the literature and are ready to synthesize your information, be careful to adequately give credit to original authors by citing appropriately.  This is a critical skill that all public health professionals must develop. The general convention is: “when in doubt, cite” (1). There is no such thing as “over-citing,” so cite the original source as much as possible.

You must cite the source every time you incorporate research, words, ideas, data, or information that is not your own (2). While you are synthesizing and often summarizing many pieces of information, you must cite any concept that is not your own. This includes any source that contributes, either directly or indirectly, to your knowledge and understanding of the material and the formulation of your arguments (3).

Here are five basic principles to guide in you in the citing process:

  1. Quoting (1). Any time that you use the exact words of the source author, you must provide in-text citations. The wording should be in quotations to denote that it is not your original work. Use quoting sparingly, as instructors want to read your understanding and synthesis of the material, not your ability to extract meaningful quotes. The general convention is to quote only when you could not possibly explain the concept any better in your own words. You should not quote more than three lines of text (1).
  2. Paraphrasing (1). Paraphrasing requires that you rephrase or restate the original idea. You should not simply substitute key phrases with synonyms and call it your own idea. Even if you do not directly quote a sentence and instead choose to paraphrase it, this still requires a citation. Paraphrased sentences are generally the same length as the original text (1).
  3. Summarizing (1). Summaries also require a citation, as you are still borrowing original ideas from the author. Summaries are generally shorter than the original text, and address salient topics presented by the original author (1). Citations should occur in each sentence that includes unoriginal material. Even if your entire paragraph is a summary, you should cite in each sentence rather than at the end of the paragraph.
  4. Facts, statistics, dates, and information (1). Any time you use facts, statistics, dates, or unoriginal information, you should cite the source. It is particularly important to build your arguments from reliable sources. For example, a statistic from the U.S. Census holds more weight than a Facebook poll. Seek out credible sources when including these items in your writing.
    • Note: For general knowledge or well-known facts, you may not need to cite a source. See the “When NOT to Cite” section below.
  5. Indebtedness (3). If a particular text contributed to your understanding of the material or in the formulation of your arguments, you must cite the source even if you do not directly reference it in the text. This includes anyone that helped you in clarifying your arguments, such as key informants or other correspondents (3). This can be in your bibliography, or in the form of an acknowledgements section (3).

When NOT to Cite

It is best practice to cite whenever possible. However, there are certain instances in which citing may not be necessary. Below are some examples in which you may not need to cite. However, if you are in doubt, it is best to cite the source and consult your instructor.

  • Common knowledge (2,3). Common knowledge includes facts that are found in many sources. In general, if a fact can be found in five credible sources, a citation is not necessary (4). For example, you would not need to cite that the Declaration of Independence was signed in 1776, or that water is comprised of hydrogen and oxygen.
  • Generally accepted or observable facts (2,4). When a fact is generally accepted or easily observable, you do not need a citation. For example, “smoking may be bad for your health” or “most people use cell phones” are both generally accepted and easily observable. Be careful, however; if you venture into more specific knowledge, you should cite a source. For example, if you want to provide specific numbers of teenagers that text while driving or the incidence of lung cancer among smokers, these require citations.
  • Original ideas and lived experiences (4). When writing about yourself or your lived experiences, a citation is not necessary. Original ideas, including the write-up of results from your own research or projects, do not require citations.

Additional Resources

For more information on avoiding plagiarism, visit the Understanding Plagiarism section of the Writing Guide and check out the SPH Plagiarism Tutorial. You may also wish to check out these resources:


  1. Academic Integrity. When to Cite Sources [Internet]. Princeton University. 2012 [cited 2015 Jun 24]. Available from: http://www.princeton.edu/pr/pub/integrity/pages/cite/
  2. Oxford College Library. Citing Your Sources [Internet]. Emory Libraries & Information Technology. [cited 2015 Jun 24]. Available from: http://oxford.library.emory.edu/research-learning/citation-plagiarism/citing.html
  3. When to Cite Sources [Internet]. Columbia College. [cited 2015 Jun 24]. Available from: https://www.college.columbia.edu/academics/whentocite
  4. Stolley K, Brizee A, Paiz J. Is It Plagiarism Yet? [Internet]. Online Writing Lab. 2013 [cited 2015 Jun 24]. Available from: https://owl.english.purdue.edu/owl/resource/589/2/

Learn more about BUSPH Public Health Writing