Changes in clinical trials mandated by the advent of meta-analysis.

Service on the Data Monitoring Committee of the CPEP (Calcium for Pre-eclampsia Prevention) has led us to four conclusions about clinical trials which we should like to present to this gathering of biostatisticians for their reactions: (i) meta-analyses of the pertinent published trials of the same therapy should always be undertaken before the start of a new trial, and the results examined to help determine the design of a new trial or determine if a trial should be undertaken at all; (ii) assuming that a decision is made to go ahead, the results of the past trials should be used in sizing the new one; (iii) in the course of the new one, regardless of the size estimates, stopping early should be considered if the trends conform to the results of the meta-analysis; and (iv) heterogeneity of patients entering clinical trials is desirable and should be specifically studied, and it should never be concluded that an average outcome is applicable to all future patients.