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February 5, 1997

Large Trials vs Meta-analysis of Smaller Trials

JAMA. 1997;277(5):377. doi:10.1001/jama.1997.03540290029025

To the Editor.  —The article by Dr Cappelleri and colleagues1 suggests that larger trials and meta-analyses of smaller medical intervention studies typically yield the same result. Although assumptions in conventional statistical power analysis predict that large trials gauging a population effect yield parallel results to aggregated smaller trials, questions of treatment integrity yield a different prediction. For example, larger studies may involve more personnel who are less likely to be trained as scientists or who may be less concerned with the scientific integrity of the trial. The hypothesis that larger studies should produce smaller effects is best tested by examining treatment magnitude as a continuous function of the sample size, an analysis that Cappelleri et al did not report.Recent meta-analyses of behavioral intervention studies examining health-risk behaviors provide another opportunity to test this hypothesis. Our search of MEDLINE (1966 through December 1996) and other databases (eg, PsychLIT, January 1974 through September