Changes in beliefs identify unblinding in randomized controlled trials: a method to meet CONSORT guidelines

In view of the relative insensitivity of cross-sectional measures, the minimal additional information in more than two assessments of beliefs and the risk of modifying participants' beliefs by repeated questioning, we conclude that the optimal means of assessing unblinding is an intergroup comparison of the change in beliefs (and not their correctness) between the start and end of a randomized controlled trial.