A clinician's guide to systematic reviews.

The purpose of this article is to discuss systematic reviews, how they are performed, and their associated strengths and limitations. A systematic review is an assessment of evidence involving exact methods to systematically identify, select, and critically evaluate all available literature on a particular topic. Unlike most narrative reviews, systematic reviews have defined methods established a priori for searching, evaluating, extracting, synthesizing, and reporting available evidence. Key characteristics differentiating systematic reviews from most narrative reviews include: clearly stated objectives, pre-defined inclusion/exclusion criteria, an explicit reproducible methodology, systematic exhaustive searches to identify all sources of evidence, an assessment of the validity for each included study, and a systematic presentation of the study characteristics/results. Though there are significant advantages to systematic reviews, there are also clear limitations such as: the quality of included evidence; heterogeneity and homogeneity of included studies; and publication bias. Even with these limitations, systematic reviews are beneficial to front line clinicians when the quantity of evidence is so substantial that reviewing and synthesizing it is not feasible, available evidence is conflicting, or when the robustness of available evidence is unknown.