title: The risk of unblinding was infrequently and incompletely reported in 300 randomized clinical trial publications.
abstract: OBJECTIVE
  To assess the proportion of clinical trials explicitly reporting the risk of unblinding, to evaluate the completeness of reporting on unblinding risk, and to describe the reported procedures involved in assessing unblinding.
  
  
  METHODS
  We sampled at random 300 blinded randomized clinical trials indexed in PubMed in 2010. Two authors read the trial publications and extracted data independently.
  
  
  RESULTS
  Twenty-four trial publications, or 8% (95% confidence interval [CI], 5, 12%), explicitly reported the risk of unblinding, of which 16 publications, or 5% (95% CI, 3, 8%), reported compromised blinding; and 8 publications, or 3% (95% CI, 1, 5%), intact blinding. The reporting on risk of unblinding in the 24 trial publications was generally incomplete. The median proportion of assessments per trial affected by unblinding was 3% (range 1-30%). The most common mechanism for unblinding was perceptible physical properties of the treatments, for example, a difference in the taste and odor of a typhoid vaccine compared with its placebo.
  
  
  CONCLUSIONS
  Published articles on randomized clinical trials infrequently reported risk of unblinding. This may reflect a tendency for avoiding reporting actual or suspected unblinding or a genuine low risk of unblinding.
authors: The Nordic Cochrane Centre, Rigshospitalet, Department 7811, Blegdamsvej 9, 2100 Copenhagen Ø, Denmark. Electronic address: drsegunbello@yahoo.com.
authors: Segun
authors: S
authors: Bello
authors: The Nordic Cochrane Centre, Rigshospitalet, Department 7811, Blegdamsvej 9, 2100 Copenhagen Ø, Denmark.
authors: Helene
authors: H
authors: Moustgaard
authors: The Nordic Cochrane Centre, Rigshospitalet, Department 7811, Blegdamsvej 9, 2100 Copenhagen Ø, Denmark.
authors: Asbjørn
authors: A
authors: Hróbjartsson
mesh_terms: D030881:Disclosure; D006801:Humans; D011642:Publications / Q000592:standards*; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012306:Risk
keywords: Blinding; Designs; Masking; Methods; Randomized clinical trials; Reporting; Unblinding