An empty review is a systematic review that finds no studies meeting its eligibility criteria, and it still requires a complete PRISMA flow diagram ending in an included count of zero. Far from being a failure, a well-documented empty review is a legitimate and publishable result: it demonstrates a genuine evidence gap. The flow diagram is what proves the gap is real rather than the product of a thin search, so every box from identification down to inclusion must be filled in exactly as you would for any other review. You can build the figure, zero included studies and all, in our free PRISMA 2020 flow diagram generator.
The instinct of many researchers facing an empty result is to abandon the diagram or leave boxes blank. That is the wrong move. The transparency of the figure is precisely what gives an empty review its scientific value.
Why an Empty Review Still Needs a Full Diagram
A systematic review answers a question by searching comprehensively and screening transparently. When the answer is "no eligible studies exist", that conclusion is only credible if the search and screening were thorough. The flow diagram is the evidence of thoroughness.
A complete diagram shows that you searched multiple databases, screened a substantial number of records, assessed full texts, and excluded each one for a documented reason that maps to your eligibility criteria. Without it, a reader cannot distinguish a true evidence gap from an underpowered search. Our guide on how to conduct a systematic review sets out the methodological steps that make an empty result defensible.
Completing Each Box Down to Zero
The diagram for an empty review is filled in normally until the final stage:
- Identification: report the full search yield per database and any other sources, exactly as you would for a populated review.
- Records removed before screening: deduplicate and record the count removed.
- Screening: report records screened and excluded at title and abstract.
- Retrieval: report reports sought and any not retrieved.
- Eligibility: report the full texts assessed and excluded, each grouped under a specific reason with its count.
- Inclusion: the studies-included box reads 0.
The key is that the eligibility exclusion reasons must account for every full text you read. If you assessed twelve reports and included none, your exclusion reasons must sum to twelve. Mismatched totals are a frequent flag, as our guide to common PRISMA diagram mistakes explains, and they are even more conspicuous in an empty review where the final number is zero.
Documenting the Final Exclusions Carefully
Because no study survives to inclusion, the exclusion reasons at the full-text stage carry the entire weight of the result. Make them specific and tied to your protocol:
- "Wrong population (n = 4)"
- "Wrong intervention (n = 3)"
- "Wrong comparator (n = 2)"
- "Wrong study design (n = 3)"
A reader should be able to see that studies were excluded for principled, pre-specified reasons rather than because the search missed them. This is the single most important element of an empty review's credibility.
What Journals and Reviewers Expect
Editors increasingly recognise empty reviews as valuable, and several journals publish them explicitly. Reviewers will look for three things: a search comprehensive enough to support a "no evidence" claim, a flow diagram that reconciles cleanly to zero, and a discussion that frames the gap as a research priority rather than a dead end.
It also helps to confirm that your screening was reliable, since a missed eligible study would undermine the whole conclusion. Our guide to systematic review screening best practices covers dual screening and agreement checks that strengthen an empty result.
Writing the Narrative Around a Zero
The text accompanying the diagram should:
- State plainly that no studies met the inclusion criteria.
- Summarise what was excluded and why, referencing the flow diagram counts.
- Discuss whether the criteria were appropriately broad, and what would need to change for evidence to exist.
- Frame the gap as a call for primary research.
This narrative, anchored by a transparent diagram, turns an empty result into a useful contribution. If broadening the question is an option, a scoping review sometimes suits an emerging topic better, a distinction our comparison of review types touches on through the step-by-step systematic review guide.
Frequently Asked Questions
Do I still need a PRISMA flow diagram if no studies were included?
Yes. The flow diagram documents that your search and screening were thorough, which is what makes a "no eligible studies" conclusion credible. The included box simply shows zero.
Can you publish a systematic review with zero included studies?
Yes. Empty reviews are publishable and valued because they identify genuine evidence gaps. Several journals explicitly welcome them, provided the search is comprehensive and the reporting is transparent.
How do I fill in the exclusion reasons for an empty review?
Group every full-text report you assessed under a specific, protocol-based reason with its count, and make those counts sum to the total reports assessed. In an empty review these exclusions carry the entire result, so specificity matters.
Is an empty review a failed review?
No. A rigorously conducted empty review is a legitimate finding that maps an evidence gap and signals where primary research is needed. The rigour of the method, shown by the flow diagram, is what determines its value.
What if I worry my search missed studies?
Strengthen confidence by searching multiple databases, adding citation searching, and using dual independent screening with an agreement check. Documenting these steps reassures reviewers that the empty result reflects a true gap rather than an incomplete search.