[Contributions of systematic review and meta-analysis to public health].
Meta-analysis has several precedents; even in Confucius (VI BC) one can find a sentence about the synthesis of knowledge. Meta-analysis is a consequence of the paradigm of induction. Within this paradigm of research, meta-analysis gives an analysis of the principle of consistency of a causal association (2nd principle of Hill). It has promoted the development of evaluation questionnaires and protocols for different designs, mainly clinical trials. It favoured the movement of evidence-based medicine, which is behind the creation of agencies for the evaluation of health technologies, and the recognition of public health professionals dedicated to research methods (mainly epidemiologists). The contributions of meta-analysis to public health are not distinguishable from others made to other specialties, although in the field of research methods it has contributed to the study of publication bias and to the search of determinants of heterogeneity, the lack of consistency among the individual studies.