Where now for meta-analysis?

In the short time since its introduction, meta-analysis, the statistical pooling of the results from independent but ‘combinable’ studies, has established itself as an influential branch of clinical epidemiology and health services research, with hundreds of meta-analyses published in the medical literature each year. 1 This issue of the International Journal of Epidemiology contains several papers 2‐9 that address methodological issues in metaanalytic research, a review article on where we stand with systematic reviews in observational epidemiology 10 and three meta-analyses of observational studies. 11‐13 Publication of a themed issue on meta-analysis by an epidemiological journal begs several questions: Where does meta-analysis come from? Does it deserve the attention it is currently getting? And where should it be going next? The statistical basis of meta-analysis reaches back to the 17th century when, in astronomy, intuition and experience suggested that combinations of data might be better than attempts