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

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.