BMJ  2004;328:1135-1136 (8 May), doi:10.1136/bmj.328.7448.1135-b

Letter

Turning a blind eye

Authors have blinkered view of blinding

The first 150 words of the full text of this article appear below.

EDITOR—Fergusson et al 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.1 They are quite wrong to do so.

R A Fisher (1890-1962)

Credit: A C BARRINGTON BROWN

The whole point of a successful double blind trial is that there should be unblinding through efficacy. That is to say that there should be no incidental reasons, apart from efficacy, as to why the treatments are distinguishable but that the treatments should reveal themselves through efficacy. If the treatments are not distinguishable at all, then the treatments have not been proved different.

The classic description of a blind experiment is Fisher's account of a woman tasting tea to distinguish which cups have had milk in first and which cups have had tea in first in support of her claim that the . . . [Full text of this article]

Stephen J Senn, professor of statistics

University of Glasgow, Glasgow G12 8QQ stephen@stats.gla.ac.uk


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Relevant Article

Turning a blind eye: the success of blinding reported in a random sample of randomised, placebo controlled trials
Dean Fergusson, Kathleen Cranley Glass, Duff Waring, and Stan Shapiro
BMJ 2004 328: 432. [Abstract] [Full Text] [PDF]

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