Subgroup analysis in randomized controlled trials appeared to be dependent on whether relative or absolute effect measures were used
SourceJournal of Clinical Epidemiology, 67, 4, (2014), pp. 410-415
Article / Letter to editor
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Journal of Clinical Epidemiology
SubjectRadboudumc 15: Urological cancers RIHS: Radboud Institute for Health Sciences
OBJECTIVES: To assess whether relative or absolute effect measures were used in subgroup analyses of randomized controlled trials (RCTs) and study whether conclusions would change if subgroup effects were calculated on a different scale than reported. STUDY DESIGN AND SETTING: We studied all 327 RCTs published in 2010 in five major medical journals. For trials with a dichotomous primary outcome, we extracted reported main and subgroup effect measures. If crude subgrouping data were reported, we calculated the subgroup effects on both relative and absolute scales. RESULTS: Of the 229 RCTs with a dichotomous primary outcome, 120 (52%) performed subgroup analyses. In 106 of these 120 (88%) RCTs, relative effect measures were used for subgroup analyses, whereas an absolute scale was used in 9 (8%) trials. Two (2%) RCTs reported both relative and absolute subgroup effects. Crude data of the subgroups could be extracted in 41 of the 120 (34%) RCTs. Calculating subgroup effects on a different scale than reported lead to a change in conclusion in 17% of the 41 trials. CONCLUSION: Almost all RCTs used relative effect measures for subgroup analyses. Interpretation of subgroup effects, however, appeared to be dependent on whether relative or absolute effect measures were used.
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