title: Validity of indirect comparison for estimating efficacy of competing interventions: empirical evidence from published meta-analyses.
abstract: OBJECTIVE
  To determine the validity of adjusted indirect comparisons by using data from published meta-analyses of randomised trials.
  
  
  METHODS
  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.
  
  
  METHODS
  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 (P<0.05) was observed in three of the 44 comparisons between the direct and the adjusted indirect estimates. There was a moderate agreement between the statistical conclusions from the direct and adjusted indirect comparisons (kappa 0.51). The direction of discrepancy between the two estimates was inconsistent.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Public Health and Epidemiology, University of Birmingham, Birmingham B15 2TT. f.song@bham.ac.uk
authors.forename: Fujian
authors.initials: F
authors.lastname: Song
authors.forename: Douglas G
authors.initials: DG
authors.lastname: Altman
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Glenny
authors.forename: Jonathan J
authors.initials: JJ
authors.lastname: Deeks
mesh_terms: D003627:Data Interpretation, Statistical; D016555:Matched-Pair Analysis; D015201:Meta-Analysis as Topic; D016032:Randomized Controlled Trials as Topic; D015203:Reproducibility of Results; D013812:Therapeutics; D016896:Treatment Outcome