title: Subgroup analysis in randomized controlled trials appeared to be dependent on whether relative or absolute effect measures were used.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  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.
authors: Department of Otorhinolaryngology, University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands; Julius Center for Health Sciences and Primary Care, University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands. Electronic address: R.P.Venekamp@umcutrecht.nl.
authors: Roderick P
authors: RP
authors: Venekamp
authors: Julius Center for Health Sciences and Primary Care, University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands; Department of Health Evidence, Radboud University Medical Center Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands; Department of Operating Rooms, Radboud University Medical Center Nijmegen, PO Box 9101, 6500 HB Nijmegen, The Netherlands.
authors: Maroeska M
authors: MM
authors: Rovers
authors: Julius Center for Health Sciences and Primary Care, University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands.
authors: Arno W
authors: AW
authors: Hoes
authors: Julius Center for Health Sciences and Primary Care, University Medical Centre Utrecht, PO Box 85500, 3508 GA Utrecht, The Netherlands.
authors: Mirjam J
authors: MJ
authors: Knol
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000379:methods* / Q000592:standards; D040242:Risk Reduction Behavior; D016896:Treatment Outcome
keywords: Absolute risk reduction; Epidemiology; Randomized controlled trials; Relative risk reduction; Subgroup analysis; Treatment effects