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In this issue ofTHE JOURNAL, Jeng et al1report discrepancies between the results of meta-analyses using aggregate data available from the literature (MAL) and meta-analyses using individual patient data (MAP). This may be seen as further grounds for mistrusting meta-analysis in general2,3and MAL in particular,4but before deciding that all meta-analyses are an exercise in "mega-silliness,"5consider the alternatives. See also p 830. The key characteristic of MAPs is the use of individual patient data (IPD). Meta-analyses using aggregate data also can, and frequently do, include unpublished data, so the termIPD meta-analysesis preferable to avoid confusing issues relating to using IPD and issues relating to using unpublished data. IPD meta-analyses require international cooperation between the individuals and groups who have conducted relevant trials and a considerable amount of time, personnel, and financial resources.6These global collaborative endeavors have yielded important information
A. D. Oxman (Wed,) studied this question.