Turning a blind eye: the success of blinding reported in a random sample of randomised, placebo controlled trials

Objective To examine the reporting and success of double blinding in a sample of randomised, placebo controlled trials from leading general medicine and psychiatry journals. Methods Identification of placebo controlled, randomised controlled trials from prespecified general medical and psychiatric journals indexed on Medline between I January 1998 and I October 200 1, from which a random sample of 200 randomised clinical trials was chosen, of which 191 trials were evaluated. Results Only seven of the 97 (7%) general medicine trials provided evidence on the success of blinding, with five reporting that the success of blinding was imperfect In trials from psychiatric journals, the success of blinding was reported in eight of the 94 trials, with four reporting that the blinding was imperfect. Overall, only four of the 191 (2%) trials assessed blinding in the participants and either the outcome assessors or the investigators. Conclusions The current lack of reporting on the success of blinding provides little evidence that success of blinding is maintained in placebo controlled trials. Trialists and editors should make a concerted effort to incorporate, report, and publish such information and its potential effect on study results.