Systematic review
A rigorous, reproducible survey of all the evidence on a question.
What it means
A systematic review is a structured synthesis that uses explicit, pre-specified methods to locate, appraise, and summarize all studies relevant to a clearly framed question. Its defining features are a comprehensive search strategy, transparent inclusion and exclusion criteria, and formal assessment of each study's risk of bias, all documented so the review can be reproduced and updated. By minimizing the arbitrariness of traditional narrative reviews, it aims to give an unbiased picture of the evidence base. A systematic review may or may not include a meta-analysis; when the studies are too heterogeneous to pool, the synthesis remains qualitative.
Examples
Following a registered protocol, reviewers screen thousands of abstracts against fixed criteria to summarize every trial of a school intervention.
Before searching a single database, the team registers its question, sources and inclusion rules on PROSPERO, so nobody can quietly drop the trials that came out the wrong way.
Asked whether standing desks ease back pain, reviewers search four databases, keep only randomised trials, appraise each for bias — then report that the trials are too different to pool.
First described in Evidence-based medicine; Cochrane Collaboration (1993); Archie Cochrane (1972).