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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 1 January 1998 and 1 October 2001, 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.
Although the definition of double blind varies, (1) we consider a trial to be double blind when the patient, investigators, and outcome assessors are unaware of the patient's assigned treatment throughout the conduct of the trial. (2) Placebos are commonly used as an inactive treatment to achieve double blinding, especially when no existing effective treatment is available. Sometimes, placebos are proposed instead of a standard existing treatment or standard care to ensure assay sensitivity. This is the ability of a trial to distinguish effective interventions from ineffective interventions. It depends on the effect size that is to be detected, so the investigators need to know …