Methods for combining randomized clinical trials: Strengths and limitations


  • David L. Demets

    1. Department of Statistics and University of Wisconsin Clinical Cancer Center, Room 6749 Medical Science Center, 420 North Charter Street, Madison, Wisconsin 53706, U.S.A.
    Search for more papers by this author


Methods for combining data from several studies exist and appear to be quite useful. None satisfactorily addresses the question of what studies should be combined. This issue is the most serious methodological limitation. Even studies with statistically significant interaction might still be combined if the effect were in the same direction. Thus, substantial scientific input is required as to what criteria must be met by each potential study. Much can be learned from combining or pooling data but it must be done cautiously. Pooling exercises do not replace well designed prospective clinical trials. Efforts for establishing basic design criteria to allow for multicentre and multicountry trials to be more easily combined might be useful.