REPLY
Blinding in Placebo-Controlled Trials
Norman A. Desbiens, MD
19 June 2001 | Volume 134 Issue 12 | Page 1151
IN RESPONSE:
The motivation for my editorial was not to detract from the work of Dr. Prasad and colleagues (1) but rather to suggest a method that would allow them to use their data on the guess to better understand their findings. Was it the zinc, the suspicion that participants were taking zinc, or both that led to the demonstrated "reduced duration and severity of cold symptoms"? Using regression analysis with duration of cold symptoms as the dependent variable and allocation (placebo/zinc) and the guess (zinc/don't know/placebo) as independent variables would have strengthened the authors' analysis by giving them insight into whether unblinding could have confounded their interpretation. A further refinement would have been the inclusion of an interaction term to see whether different effects were observed depending on differences in the guess, although the study included too few patients to allow this. Dr. Ehrlich indicates that psychological factors "seem to play a major confounding role in our assessment of disease course." However, an adequate number of participants and proper analysis of data on the guess could give us a better understanding of the influence of these factors on the outcomes of randomized trials.
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Author and Article Information
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University of Tennessee College of Medicine—Chattanooga Unit; Chattanooga, TN 37403 (Desbiens)
1. Prasad AS, Fitzgerald JT, Bao B, Beck FW, Chandrasekar PH. Duration of symptoms and plasma cytokine levels in patients with the common cold treated with zinc acetate. A randomized, double-blind, placebo-controlled trial Ann Intern Med. 2000;133:245-52. [PMID: 10929163].[Abstract/Free Full Text]
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