The Pocket Guide to Critical Appraisal. Iain K. Crombie

because of their small size, can be greatly affected by the play of chance.

      Essential features

      Systematic reviews search electronic databases of research studies, such as MEDLINE, EMBASE, and CINAHL, to locate published studies, using carefully chosen combinations of key terms. Papers are carefully screened to identify the relevant ones. The chosen papers are commonly referred to as the primary studies. Key data items, such as effect size, standard deviation, and sample size, are extracted from each study. These data are usually, but not always, combined to provide an overall estimate of effect size using meta‐analysis.

      Complications

There are no complications. The design of a systematic review differs substantially from all other types of study, so that an inspection of the methods used should identify it.

      Terms of identification

      Either of the terms systematic review or meta‐analysis identifies the design. If there is doubt, then the use of a search strategy should provide confirmation. The terms review and narrative review can refer to a systematic review or to a study with a less complete collection of primary studies. An overview usually indicates a collection of systematic reviews, but it can be used for a set of primary studies.