Defining a Gap in the Literature: On Proving the Presence of an Absence -->

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Defining a Gap in the Literature: On Proving the Presence of an Absence

It’s standard in any study to point out the gap in the literature you're seeking to fill. (Else why do the study—unless it’s a replication study?) Like the hole in the donut, the gap is defined by what surrounds it. Yet it’s common to read statements in the literature review such as (a) “I could not find anything on [the issue] in the literature” or (b) “Very few studies, if any, talked about [the issue].”

Walden Writing Center Blog on defining a gap in the literature

The problem with (a) is that it raises a series of questions in the reader’s mind: If you couldn’t find anything, gee, where did you look? What databases did you use? What keywords did you use? What was your time range? What exactly did you find? Reporting your search strategy should cover all but the last question.

It’s not easy to prove a negative: This does not exist. Therefore, to define a gap, a precise and exhaustive search is needed to identify all the studies around—but not touching—your topic. Reporting what you did find, what is known (the donut) implies what is not known (the hole in the donut). The unknown is the gap, your topic.

The problem with (b) is that it leaves readers wondering about what you know; it asks them to just accept your claim with no support. If your search were thorough, you would know whether any or just a few studies talked about your issue. If there were none, then, just as in (a), you’d define the gap by identifying the studies around—but not touching—your precise topic. The number of studies required to make that point could vary. However, if there were some studies, then you'd need to discuss only those studies in order to confirm for your readers that something was indeed missing—your angle on the issue.

If your search was precise—if you named all the databases you used (not just the names of portals, such as ProQuest or EBSCO), if you listed all the keywords (not phrases) you used, and if you specified your time range—then your committee (and future readers) could have confidence that you were in the right ballpark. If you then described what was known—using a broad set of studies or a handful of specific studies—then your readers could have confidence in your claim because they could see your process, and judge the data adduced, to “prove” a negative and reveal the presence of an absence.


Tim McIndoo
, who has been a dissertation editor since 2007, has more than 30 years of editorial experience in the fields of medicine, science and technology, fiction, and education. 

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  1. Thanks for this wonderful post on how to define the donut "hole." I have started sending this link to my students at the prospectus and literature review phase! It is known affectionately in our mentor group as "the donut post" ~Dr. Darci

    1. "The donut post"--we love it! Thanks for sharing, Dr. Darci. It's so great to hear from faculty and students who find our posts helpful.

    2. Yes. Dr. Harland just sent this to me. Thank you Dr. Harland.

    3. Great to hear--glad that you find this useful!

  2. Thank you for this information, however, it doesn't seem to give a good description of what a Gap is, only what it isn't.

    1. Thanks for the comment! Yes, the tricky thing about gaps is that they are "absences" (i.e., things that are "not"), and thus frustrate attempts at positive definitions.