How many references is enough?

Like most senior academics I am reviewing a lot of papers, both for journals where I am on the editorial board and for my junior colleagues in the context of my staff development work at Middlesex. Many of these papers have sentences followed (or interrupted in the middle) by a long and sometimes very long string of references. Most of these papers had well over 100 references in total, which might even lead the paper to be inaccurately classified as a review article by the Web of Science. So I started wondering: How many references is enough?

More isn't always better

My "rule of thumb" has always been to use a maximum of three references to support a particular statement. The role of a literature review is to provide a targeted review of the literature.  In my view, there are several reasons why it is wise not to use too many references:

  1. It really disturbs the flow of the paper.
  2. It may provide an implicit signal that your work isn't very interesting or important, as so much has already been published in the field. This means you need to work harder to convince the reviewers you are making a unique contribution.
  3. It shows that you may not be able to distinguish what the key works in a particular field are and thus are not really that well versed in the literature.
  4. It does make you look like a bit of a student as having lots of references is quite typical of PhD theses. So it might lead the reviewer to think you are an immature academic writer, which is something you would want to avoid.
  5. The more references you use (beyond the ones that are really needed to substantiate your argument), the higher the risk that one of the reviewer knows the work you cite better than you do and disagrees with you that this work supports the statement(s) you are making. This might lead the reviewers to be more critical of the rest of the paper as well.

The other side of the coin

On the other hand, there are also good reasons to not be stingy with references.

  1. You need to demonstrate your thorough knowledge of the field by citing enough of the key references. If the field has been very active, this might mean referencing quite a lot of studies.
  2. You need to cite the "key people" in a particular field for both intrinsic (this is what is expected in a literature review) and extrinsic reasons (they might be your reviewers and might be annoyed if you have missed their work). However, unless they are intrinsically important, don't "slip in" some references to people you think might be your reviewers by adding them to a block of other references. I have lost count of the number of times a reference to my work really had nothing to do with the content (see also Are referencing errors undermining our scholarship and credibility?).
  3. You need to show you are part of the journal "conversation" (see also Why does my paper get a desk-reject time and again?). Again do this only when the references are intrinsically important. Editors are not stupid, they can  spot easily that you have just added references to their journal last minute after having been rejected at your preferred journal.

General recommendations

As always, looking at your target journal will give you a better feel of the preferences in your sub-discipline (for details of this principle see the slides here: Middlesex University Summer 2019 writing boot-camp). When doing a final read of the paper, you might also want to reconsider deleting references that you are only citing once and only in connection with a lot of others. These are clearly not essential to your paper. For further guidelines, refer to these - slightly edited - responses to the question: How many references do I need at https://academia.stackexchange.com/ (a very useful site). For general guidance on when to use references see one of my first white papers: Writing coursework assignments

Answer 1: The short and somewhat unsatisfactory answer is: enough

There is no formal limit but obviously too many becomes impractical. If you can reference a huge number of references for a single statement (sentence) it is normal to pick one or possibly a few by using a format indicating these references are just examples, "e.g., Smith et al., 1943; Turner and Anthony, 1963)", "[some statement] by, for example, Smith et al. (1943) and Turner and Anthony (1963)."

Exactly when it is reasonable to show examples and when one actually have to show all references is a matter of context. If you, for example, have a series of references that together build up some matter and where none is more important than the other and none summarize the other, it could be necessary to list them all regardless of how many there are. I suggest you try to look at a number of different papers of a similar type (literature review) to the one you are writing to see how others handle such instances. [...]

The main point of this is to know when it is sufficient to list only (good) examples rather than all possible references. This is of course a matter of training and learning to assess when which format is appropriate. It is therefore necessary to assess when papers simply duplicate each other (from whatever view point you reference) or when they each contribute something unique that merits their reference.

Answer 2: Don't over do it

A literature review in an article is meant as a general reference, so the reader can get "up to speed" in the state of the art of the topic under discussion. In your thesis, you have to show that you are able to search the literature, you understand it, and are able to extract the important information. If you put every single article, you are not fulfilling any. On the one hand, the reader will not know what are the most relevant articles for your work. On the other front, anyone can get all the articles published in a subfield in the last couple of years and write a sentence, based on the abstract and the figures, in just a few days. In short, show that you have comprehended the literature by finding the most informative subset of articles.

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