# Systematic review

A systematic review answers one clearly stated question by finding, appraising and summarising every study that meets pre-set criteria. What makes it systematic is the protocol: question, databases, search terms, inclusion rules and analysis plan are fixed before any result is seen, and usually registered in PROSPERO. Two reviewers screen titles and full texts independently and settle disagreements openly. Each included study is graded for risk of bias, with RoB 2 for randomised trials and ROBINS-I for non-randomised ones. Reporting follows the PRISMA 2020 statement, a 27-item checklist whose flow diagram records how many reports were found, screened and excluded, and why. A meta-analysis is optional. When populations, doses or outcomes differ too much to pool, the review reports a structured narrative synthesis instead of a single number. The method grew out of Archie Cochrane's 1972 critique of unevaluated medical practice and became routine after the Cochrane Collaboration formed in 1993. The failure mode is a rigorous process applied to a weak literature, which yields a conclusion that looks more certain than it is. In longevity research, where single trials are short and small, systematic reviews are the standard unit of evidence behind recommendations.

## Sources

- Page MJ, McKenzie JE, Bossuyt PM, et al.. (2021). The PRISMA 2020 statement: an updated guideline for reporting systematic reviews. BMJ. https://doi.org/10.1136/bmj.n71
- Chalmers I, Hedges LV, Cooper H. (2002). A Brief History of Research Synthesis. Evaluation & the Health Professions. https://doi.org/10.1177/0163278702025001003
- Sterne JAC, Savović J, Page MJ, et al.. (2019). RoB 2: a revised tool for assessing risk of bias in randomised trials. BMJ. https://doi.org/10.1136/bmj.l4898
- Shea BJ, Reeves BC, Wells G, et al.. (2017). AMSTAR 2: a critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both. BMJ. https://doi.org/10.1136/bmj.j4008

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_Canonical: https://longevity-germany.com/en/glossary/systematic-review · Part of Longevity Cities · Updated 2026-08-25_