Turning a blind eye

Editor—Reports of randomised trials should state clearly whether blinding was attempted, and if so who was blinded and how this was done.¹ Fergusson et al note that blinding may be ineffective in some trials, making them less sound methodologically than they seem to be.²

But trial participants asked to guess the treatment they received might well be influenced by outcome. We might expect to see an apparent breaking of the blind more often in trials when the effect of treatment was a marked, for either an intended outcome or adverse effect. Indeed, end of trial tests of blindness might be tests of hunches for adverse effects or efficacy.³,⁴ Assessments of blinding success would be much more reliable in trials when they can be carried out before the clinical outcome has been determined.

Furthermore, those who successfully decipher assignments may disguise their unblinding actions.³,⁴ That difficulty, along with the aforementioned interpretational difficulties, lead us to question the usefulness of blinding tests in some circumstances.

The CONSORT statement recommends reporting the findings of an assessment of blinding if it was done.⁵ Fergusson et al say that the CONSORT statement should be amended, to suggest that assessment of blinding should be done routinely. We are not convinced that all trialists should carry out such an exercise. Furthermore, CONSORT is a set of reporting recommendations—it does not make statements on how trials should be done, but asks that what was done should be fully and accurately reported.