Systematic reviews can, if done well, provide a convenient and unbiased summary of the evidence on a particular topic. The presence of substantial heterogeneity in a meta-analysis is always of interest. On the one hand, it may indicate that there is excessive clinical diversity in the studies included, and that it is inappropriate to derive an estimate of overall effect from that particular set of studies. On the other hand, appropriate exploration of the source of heterogeneity may either identify poor design of the studies included or perhaps not even identify the cause; in either case, investigating the source of the heterogeneity may be identified as a topic for future research.

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