Statistics Notes: Blinding in clinical trials and other studies

doi:10.1136/bmj.321.7259.504

BMJ 2000;321:504 ( 19 August )

Education and debate

Statistics Notes

Blinding in clinical trials and other studies

Simon J Day, manager, clinical biometrics ^a, Douglas G Altman, professor of statistics in medicine ^b.

^a Leo Pharmaceuticals, Princes Risborough, Buckinghamshire HP27 9RR, ^b ICRF Medical Statistics Group, Institute of Health Sciences, Oxford OX3 7LF

Correspondence to: S J Day
The first 150 words of the full text of this article appear below.

Human behaviour is influenced by what we know or believe. In research there is a particular risk of expectation influencingfindings, most obviously when there is some subjectivity in assessment,leading to biased results. Blinding (sometimes called masking)is used to try to eliminate suchbias.

It is a tenet of randomised controlled trials that the treatment allocation for each patient is not revealed until the patienthas irrevocably been entered into the trial, to avoid selectionbias. This sort of blinding, better referred to as allocationconcealment, will be discussed in a future statistics note. Incontrolled trials the term blinding, and in particular "doubleblind," usually refers to keeping study participants, those involvedwith their management, and those collecting and analysing clinicaldata unaware of the assigned treatment, so that they should notbe influenced by thatknowledge.

The relevance of blinding will vary according to circumstances. Blinding . . . [Full text of this article]

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