BMJ  2004;328:1136 (8 May), doi:10.1136/bmj.328.7448.1136-a

Letter

Turning a blind eye

Why we don't test for blindness at the end of our trials

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

EDITOR—I write with reference to the paper by Fergusson et al.¹ Asking patients or their clinicians at the end of a trial which drug they think they were taking confounds failures in blinding with successes in pre-trial hunches about efficacy.

Thirty years ago, at the end of the first ever trial of aspirin and sulfinpyrazone for threatened stroke, we asked our trial clinicians to predict which drug each of their patients had been assigned.² With four regimens in this "double dummy" trial, we'd expect correct predictions for 25% of patients; our clinicians' predictions were correct for only 18% of them (2P < 0.05).

This apparently nonsensical result made sense when we compared it with our incorrect pre-trial hunches that sulfinpyrazone probably was effective and aspirin probably was not. When our patients had done well, their clinicians tended to predict that they had received sulfinpyrazone; when patients had suffered . . . [Full text of this article]

Trout Research and Education Centre at Irish Lake, RR 1, Markdale, ON, Canada N0C 1H0 sackett@bmts.com

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

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A reason to be Bayesian?

Hans-Hermann Dubben
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