Systematic review

A systematic review is a structured synthesis of research that starts with a clearly defined question and follows an explicit, documented method to find, select, appraise, and summarize all eligible studies. The defining features are a pre-specified protocol, a comprehensive search across multiple sources, transparent inclusion and exclusion criteria, and an assessment of each study's risk of bias. This process distinguishes it from a narrative review, where an author may cite a convenient or favorable subset of the literature. A systematic review may or may not include a statistical pooling of results; that pooling is the meta-analysis. When reading one, check whether a protocol was registered in advance, whether the search was broad enough to catch unpublished and non-English studies, and whether the authors assessed the quality of included trials rather than just counting them. For example, a systematic review of a treatment gathers every qualifying trial, rates each for bias, and reports the overall picture, including where evidence is weak or conflicting.