How to check whether a systematic review already exists

Before you commit months to a review, make sure nobody has done it or is doing it. A short, systematic check protects you from the most common reason a review is rejected or ignored.

These steps take an afternoon. Record each search and its date as you go.

The steps

1. Write the question as population, intervention, comparator and outcome. List synonyms for each, including brand and generic drug names, abbreviations and alternative spellings.
2. Search PubMed. Combine your terms with the systematic review subset by adding systematic[sb] to the search, or use the Clinical Queries tool. Run a second search with 'meta-analysis' in the title or abstract.
3. Search the Cochrane Library for Cochrane reviews and protocols on the question.
4. Search PROSPERO, the international register of systematic reviews, for registered or ongoing reviews that are not yet published. For non-health questions, look at the Campbell Collaboration, and for other fields at registries such as OSF.
5. Search Epistemonikos, a database that collects systematic reviews and links them to the primary studies they include.
6. Search by outcome and by population separately, not only by the intervention. A review of a different drug in the same population can still answer your question.
7. Check the citations. Take two or three landmark primary studies on your question and look at which reviews cite them. Reviews that include the same key studies are your closest competitors.
8. For each close review, record the search date, the question, the number of included studies and the reliability (see AMSTAR 2 or ROBIS).
9. Decide whether to skip, update, extend or proceed, and write the reason into your protocol.

Common mistakes

• Searching only for the intervention and missing reviews of the same question under different names.
• Stopping at published reviews and missing registered protocols.
• Treating an old review as proof the topic is done, or a new one as proof that it is closed.
• Not recording the search, which makes the check impossible to repeat or defend.

Doing the check faster

SynthGap automates much of this. Its discovery step checks candidate topics against existing systematic reviews, using a citation index of reviews that cite the primary studies, and lists the studies behind each topic.

It is a first pass. Always run your own final check just before you register a protocol, since new reviews appear all the time.

Questions

Keep reading

General methodological guidance, not medical advice. SynthGap's suggestions are AI-generated from the published literature, so verify them before registering a protocol.