Understanding and evaluating systematic reviews and meta-analyses

A systematic review is a summary of existing evidence that answers a specific clinical question, contains a thorough, unbiased search of the relevant literature, explicit criteria for assessing studies and structured presentation of the results. A systematic review that incorporates quantitative pooling of similar studies to produce an overall summary of treatment effects is a meta-analysis. A systematic review should have clear, focused clinical objectives containing four elements expressed through the acronym PICO (Patient, group of patients, or problem, an Intervention, a Comparison intervention and specific Outcomes). Explicit and thorough search of the literature is a pre-requisite of any good systematic review. Reviews should have pre-defined explicit criteria for what studies would be included and the analysis should include only those studies that fit the inclusion criteria. The quality (risk of bias) of the primary studies should be critically appraised. Particularly the role of publication and language bias should be acknowledged and addressed by the review, whenever possible. Structured reporting of the results with quantitative pooling of the data must be attempted, whenever appropriate. The review should include interpretation of the data, including implications for clinical practice and further research. Overall, the current quality of reporting of systematic reviews remains highly variable.