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The Landscape and Lexicon of Blinding in Randomized Trials

Kenneth F. Schulz, PhD, MBA; Iain Chalmers, DSc; and Douglas G. Altman, DSc
[+] Article, Author, and Disclosure Information

Dr. Schulz: Family Health International, Research Triangle Park, NC 27709 Dr. Chalmers: United Kingdom Cochrane Centre, Oxford, United Kingdom OX2 7LG Professor Altman: ICRF Medical Statistics Group, Centre for Statistics in Medicine, Institute of Health Sciences, Oxford, United Kingdom OX3 7LF

Acknowledgment: The authors thank Dr. Ted J. Kaptchuk for his review of earlier drafts of this manuscript.

Requests for Single Reprints: Kenneth F. Schulz, PhD, MBA, Family Health International, Box 13950, Research Triangle Park, NC 27709.

Current Author Addresses: Dr. Schulz: Family Health International, Box 13950, Research Triangle Park, NC 27709.

Dr. Chalmers: UK Cochrane Centre, NHS Research and Development Programme, Summertown Pavilion, Middle Way, Oxford, United Kingdom OX2 7LG.

Professor Altman: ICRF Medical Statistics Group and Centre for Statistics in Medicine, Institute of Health Sciences, Old Road, Headington, Oxford, United Kingdom OX3 7LF.

Ann Intern Med. 2002;136(3):254-259. doi:10.7326/0003-4819-136-3-200202050-00022
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Blinding in medical research possesses a rich history spanning a couple of centuries (1). Most researchers and readers grasp its meaning. Unfortunately, beyond that general understanding lies confusion. In addition to terms such as “single blind” and “double blind” meaning different things to different people, some steadfastly refuse to use the term “blinding” and insist instead on the term “masking.” Others confuse blinding with other methodologic precautions, such as concealment of allocation during the process of creating comparison groups. Still others consider that randomization is of little use unless accompanied by “double-blinding,” thus revealing that they have not understood that these separate aspects of methodology address separate sources of bias.

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