title: The effects of excluding treatments from network meta-analyses: survey.
abstract: OBJECTIVE
  To examine whether the exclusion of individual treatment comparators, including placebo/no treatment, affects the results of network meta-analysis.
  
  
  METHODS
  Survey of networks with individual trial data.
  
  
  METHODS
  PubMed and communication with authors of network meta-analyses.
  
  
  METHODS
  We included networks that had five or more treatments, contained at least two closed loops, had at least twice as many studies as treatments, and had trial level data available. Investigators abstracted information about study design, participants, outcomes, network geometry, and the exclusion of eligible treatments.
  
  
  RESULTS
  Among 18 eligible networks involving 757 randomised controlled trials with 750 possible treatment comparisons, 11 had upfront decided not to consider all treatment comparators and only 10 included placebo/no treatment nodes. In 7/18 networks, there was at least one node whose removal caused a more than 1.10-fold average relative change in the estimated treatments effects, and switches in the top three treatments were observed in 9/18 networks. Removal of placebo/no treatment caused large relative changes of the treatment effects (average change 1.16-3.10-fold) for four of the 10 networks that had originally included placebo/no treatment nodes. Exclusion of current uncommonly used drugs resulted in substantial changes of the treatment effects (average 1.21-fold) in one of three networks on systemic treatments for advanced malignancies.
  
  
  CONCLUSIONS
  Excluding treatments in network meta-analyses sometimes can have important effects on their results and can diminish the usefulness of the research to clinicians if important comparisons are missing.
authors.affiliation: Faculty of Health Sciences, University of Ottawa, Ottawa, Canada. edward.mills@uottawa.ca
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Mills
authors.forename: Steve
authors.initials: S
authors.lastname: Kanters
authors.forename: Kristian
authors.initials: K
authors.lastname: Thorlund
authors.forename: Anna
authors.initials: A
authors.lastname: Chaimani
authors.forename: Areti-Angeliki
authors.initials: AA
authors.lastname: Veroniki
authors.forename: John P A
authors.initials: JP
authors.lastname: Ioannidis
mesh_terms: D002986:Clinical Trials as Topic; D006801:Humans; D015201:Meta-Analysis as Topic; D017594:Publication Bias