Meta-analysis is a systematic approach of synthesizing, combining, and analyzing data from multiple studies (randomized clinical trials1 or observational studies2) into a single effect estimate to answer a research question. Meta-analysis is especially useful if there is debate around the research question in the literature published to date or the individual published studies are underpowered. Vital to a high-quality meta-analysis is a comprehensive literature search, prespecified hypothesis and aims, reporting of study quality, consideration of heterogeneity and examination of bias. In the hierarchy of evidence, meta-analysis appears above observational studies and randomized clinical trials because it rigorously collates evidence across a larger body of literature; however, meta-analysis is largely dependent on the quality of the primary data.
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Arya S, Schwartz TA, Ghaferi AA. Practical Guide to Meta-analysis. JAMA Surg. Published online January 29, 2020. doi:10.1001/jamasurg.2019.4523
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