Rapid Evidence Assessment

Both apply transparent, replicable methods — a defined question, documented search, explicit inclusion criteria and quality appraisal. The difference is that an REA deliberately limits the breadth of one or more stages to meet a deadline, for example by searching fewer databases, restricting dates or languages, or doing less grey-literature hunting. A full systematic review aims to be exhaustive. The REA trades some comprehensiveness for speed, and it must state exactly which limits were applied so users can judge how that affects the conclusions.

It can, which is why the method insists on documenting its constraints. Restricting scope risks missing relevant studies and may bias results toward easily accessible evidence, and time pressure can shorten appraisal. The REA manages this not by pretending the shortcuts do not matter but by making them explicit and reporting the resulting limitations and confidence honestly. A well-conducted REA is far more reliable than an informal review, even if it is more provisional than a full systematic review.

When the decision is high-stakes and demands the most complete and definitive synthesis the evidence can support, and when time permits the exhaustive search and dual-reviewer rigour of a full review. An REA is often used first to scope the field and provide a timely interim answer, with a full systematic review commissioned afterwards if warranted. Where the question concerns not just whether something works but how and why, a realist synthesis may be the more suitable approach.