COMPARISON OF EFFECT ESTIMATES FROM A METAANALYSIS OF SUMMARY DATA FROM PUBLISHED STUDIES AND FROM A METAANALYSIS USING INDIVIDUAL PATIENT DATA FOR OVARIAN-CANCER STUDIES

To determine the relative merits of two quantitative methods used to e stimate the summary effects of observational studies, the authors comp ared two methods of meta-analysis. Each quantified the relation betwee n oral contraceptive use and the risk for ovarian cancer. One analysis consisted of a meta-analysis using summary data from 11 published stu dies from the literature (MAL) in which the study was the unit of anal ysis, and the second consisted of a meta-analysis using individual pat ient data (MAP) in which the patient was the unit of analysis. The aut hors found excellent quantitative agreement between the summary effect estimates from the MAL and the MAP. The MAP permits analysis 1) among outcomes, exposures, and confounders not investigated in the original studies, 2) when the original effect measures differ among studies an d cannot be converted to a common measure (e.g., slopes vs. correlatio n coefficients), and 3) when there is a paucity of studies. The MAL pe rmits analysis 1) when resources are limited, 2) when time is limited, and 3) when original study data are not available or are available on ly from a biased sample of studies. In public health epidemiology, dat a from original studies are often accessible only to limited numbers o f research groups and for only a few types of studies that have high p ublic health priority. Consequently, few opportunities for pooled anal ysis exist. However, from a policy view, MAL will provide answers to m any questions and will help in identifying questions for future invest igation.