[How to read a meta-analysis?].

Meta-analysis is aimed at assessing an exhaustive, unbiased, reproducible, quantified and accurate synthesis of a research problem. It is sustained by a systematic review of the literature and has statistical particularities. Sources of error and bias are numerous. In this paper, we describe them following the methodology steps of a well-conducted meta-analysis. Causes of divergent conclusions of meta-analyses are described and illustrated with the example of cancer risk assessment in TNF inhibitor-treated rheumatoid arthritis patients. Eventually, this article provides key-points to help readers to detect sources of error and bias in meta-analyses.