Research Gap Finder

Supervisors, journal editors and PROSPERO reviewers ask the same question before anything else: does a systematic review on this question already exist? Duplicated reviews are common enough that the problem has its own literature, and a review that repeats a recent one without a reason is hard to publish. The research gap you claim in your protocol has to survive that check, so it should be grounded in a reproducible search rather than an impression. This tool runs the first part of that search in PubMed, the free database from the United States National Library of Medicine that indexes MEDLINE, and turns the result into four numbers you can defend.

What the four numbers mean

Systematic reviews and meta-analyses counts every PubMed record on your topic that PubMed tags with its systematic review filter or as a meta-analysis. Reviews in the last three years shows whether the topic is being actively reviewed right now. Primary studies counts the original research on the topic, excluding reviews, which tells you whether there is enough evidence to synthesize at all. Randomized trials after the closest review is the number that most often reveals a gap: the newest of the five best-matching reviews stands in for the review yours would be compared against, and every randomized controlled trial published in later years is evidence that review could not include.

How the verdict is decided

The verdict follows fixed, transparent rules rather than a judgment call. Fewer than ten primary studies and fewer than three trials reads as thin evidence, where a scoping review usually fits better. Primary studies with no matching review reads as an open gap. Ten or more reviews in the last three years reads as crowded straight away. Otherwise, a closest review at least two years old with five or more trials published after it reads as an update opportunity, the situation the Cochrane Handbook describes when it discusses updating reviews as new evidence accumulates. Five or more reviews in the last three years also reads as crowded, and anything else reads as covered. These are starting points: a keyword match is not the same question, so read the closest two or three reviews before you decide.

What PubMed cannot tell you

PubMed only lists published work. A review that someone has registered in PROSPERO, the international prospective register of systematic reviews, but not yet published is invisible here, and it is the most common reason a topic that looks open turns out to be taken. Always search PROSPERO before you commit. PubMed also covers biomedicine and the life sciences; for education, social science or engineering topics, the counts will understate what exists. Finally, PubMed reads your topic with automatic term mapping to its Medical Subject Headings, so the tool shows the exact query translation for you to check and rerun.

From a gap to a protocol

Once you have an open or update-worthy topic, the next steps are the usual ones. Turn the topic into a structured PICO question, then build the full Boolean search for each database. Before registering, put the protocol into the current PROSPERO registration fields, and when the search results come back, use our free title and abstract screening workspace. For the reasoning behind gap statements, including the seven gap types and worked examples, read our guide on writing a research gap statement that holds up. If you would rather hand the whole project over, our methodologists run systematic reviews from protocol to manuscript and scoping reviews for topics with sparse evidence.