Article type
Year
Abstract
Background:
Blinding is an important methodological procedure to minimize bias in randomised clinical trials. Blinding procedures may not be effective, and loss of blinding, i.e. unblinding, occurs in an unknown proportion of trials.
Objectives:
To assess the proportion of randomised 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 300 blinded randomised clinical trials indexed in PubMed in 2010 at random. Two authors read the trial publications and extracted data independently.
Results:
Twenty-four trial publications, or 8% (95% confidence interval: 5% to 12%), explicitly reported the risk of unblinding, of which 16 publications, or 5% (3% to 8%) reported compromised blinding; and eight publications, or 3% (1% to 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% to 30%). The most common mechanism for unblinding was perceptible physical properties of the treatments, for example a difference in the taste and odour of a typhoid vaccine compared to its placebo.
Conclusions:
Published articles on randomised 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.
Blinding is an important methodological procedure to minimize bias in randomised clinical trials. Blinding procedures may not be effective, and loss of blinding, i.e. unblinding, occurs in an unknown proportion of trials.
Objectives:
To assess the proportion of randomised 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 300 blinded randomised clinical trials indexed in PubMed in 2010 at random. Two authors read the trial publications and extracted data independently.
Results:
Twenty-four trial publications, or 8% (95% confidence interval: 5% to 12%), explicitly reported the risk of unblinding, of which 16 publications, or 5% (3% to 8%) reported compromised blinding; and eight publications, or 3% (1% to 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% to 30%). The most common mechanism for unblinding was perceptible physical properties of the treatments, for example a difference in the taste and odour of a typhoid vaccine compared to its placebo.
Conclusions:
Published articles on randomised 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.