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OBJECTIVES: The methodology for the critical assessment of medical interventions is well established. Regulatory agencies and institutions adhere, in principle, to the same standards. This consistency, however, is not always the case in practice. STUDY DESIGN AND SETTING: Using the evaluation of the CAPRIE (Clopidogrel versus Aspirin in Patients at risk of Ischemic Events) trial by the British National Institute for Health and Clinical Excellence (NICE) and the German Institute for Quality and Efficiency in Health Care (IQWiG), we illustrate that there was no consensus for the interpretation of possible heterogeneity in treatment comparisons across subgroups. RESULTS: The NICE concluded that CAPRIE demonstrated clinical benefit for the overall intention-to-treat (ITT) population with sufficient robustness to possible sources of heterogeneity. The IQWiG interpreted the alleged heterogeneity as implying that the clinical benefit only applied to the subgroup of patients with a statistically significant result irrespective of the results of the ITT analysis. CONCLUSION: International standards for the performance and interpretation of subgroup analyses as well as for the assessment of heterogeneity between strata are needed.

Original publication




Journal article


J Clin Epidemiol

Publication Date





1298 - 1304


Aspirin, Cardiovascular Diseases, Clopidogrel, England, Evidence-Based Medicine, Germany, Humans, Intention to Treat Analysis, Randomized Controlled Trials as Topic, Research Design, Ticlopidine