Validity of indirect comparison for estimating efficacy of competing interventions: empirical evidence from published meta-analyses

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Abstract
Objective: To determine the validity of adjusted indirect comparisons by using data from published meta-analyses of randomised trials. Design: Direct comparison of different interventions in randomised trials and adjusted indirect comparison in which two interventions were compared through their relative effect versus a common comparator. The discrepancy between the direct and adjusted indirect comparison was measured by the difference between the two estimates. Data sources: Database of abstracts of reviews of effectiveness (1994-8), the Cochrane database of systematic reviews, Medline, and references of retrieved articles. Results: 44 published meta-analyses (from 28 systematic reviews) provided sufficient data. In most cases, results of adjusted indirect comparisons were not significantly different from those of direct comparisons. A significant discrepancy (PConclusions: Adjusted indirect comparisons usually but not always agree with the results of head to head randomised trials. When there is no or insufficient direct evidence from randomised trials, the adjusted indirect comparison may provide useful or supplementary information on the relative efficacy of competing interventions. The validity of the adjusted indirect comparisons depends on the internal validity and similarity of the included trials. What is already known on this topic Many competing interventions have not been compared in randomised trials Indirect comparison of competing interventions has been carried out in systematic reviews, often implicitly Indirect comparison adjusted by a common control can partially take account of prognostic characteristics of patients in different trials What this study adds Results of adjusted indirect comparison usually, but not always, agree with those of head to head randomised trials The validity of adjusted indirect comparisons depends on the internal validity and similarity of the trials involved