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A review of blinding in randomized controlled trials found results inconsistent and questionable
Isabelle Boutron1, Candice Estellat, Philippe Ravaud
1INSERM, U738, Paris, France. isabelle.boutron@bch.ap-hop-paris.fr
Background And Objective:
To determine methods to assess the success of blinding in randomized controlled trials (RCTs).
Methods:
We searched MEDLINE, the Cochrane Controlled Trials Register, and the Cochrane Method Register and performed a manual search to target studies that attempt to assess blinding and describe the methods used in those studies.
Results:
A total of 90 reports were selected. Reports assessed the success of blinding participants (n = 58), care providers (n = 36), and outcome assessors (n = 15). Of the 58 reports assessing the success of blinding participants, 54 (93%) reported asking participants to guess their treatment assignment. There was no consistency in timing of assessment (e.g., once at the end of the trial, 57%, or several times during the trial, 26%) or modalities of answering (e.g., "do not know" answers, 43%, or participants forced to guess, 31%). A statistical analysis was performed in 57% of reports. The statistical analysis mainly compared the proportion of correct guesses to those produced by chance (32%) or checked for a relation between participants' guesses and treatment assignment (23%).
Conclusions:
Methods of assessing the success of blinding, analysis and reporting the results were inconsistent and questionable.
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