Why are Some Meta-Analyses More Credible than Others? *

Abstract

Meta-analysis of randomized clinical trials plays an important role in summarizing all available evidence with respect to the comparison of, for example, two drugs for the same indication. Presently, meta-analysis is considered to be of only minor importance in the new drug application. This fact is astonishing; in this situation, a summary evaluation of all available evidence from many—although, in general, limited—independent clinical trials is necessary. The main reason, in our opinion, that meta-analysis is considered to be of minor importance is that presented meta-analyses often are not completely convincing because objectives are not appropriately chosen and study conduct or presentation are not sufficiently detailed to enable the reader to assess the evidence. This paper is intended to clarify why some meta-analyses have more credibility than others and to provide some guidance on increasing the credibility of meta-analyses. We believe that the ideas presented apply beyond the regulatory setting.