Meta-analyse: principes en valkuilen

Conflict of interest: none declared. Financial support: none declared.

• In a meta-analysis results of different studies are summarized quantitatively. This gives a much more precise effect estimate than is possible in individual studies.

• Prior to the analysis, all relevant studies should be traced, including studies with less favourable results. Exclusion of 'negative' studies may lead to overestimation of the effect.

• Because the results of a meta-analysis depend on the quality of the included studies, the quality and risk of bias of all studies should be systematically assessed.

• Quantitative summary of results is only practicable if the studies are homogeneous, i.e. sufficiently similar with respect to the study populations, interventions or exposure, outcomes and point of measurement.

• In cases of clinical heterogeneity, meta-analysis could be conducted in clinically homogeneous subgroups.

• Statistical heterogeneity can be discounted by using a random-effects model

• Meta-analyses can be applied to research questions regarding aetiology, diagnosis, treatment or prognosis.