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December 20, 1995

Restricted Randomization in Randomized Controlled Trials-Reply

Author Affiliations

Centers for Disease Control and Prevention Atlanta, Ga
Imperial Cancer Research Fund London, England
University of California, San Francisco

JAMA. 1995;274(23):1835-1836. doi:10.1001/jama.1995.03530230021015

In Reply.  —We thank Drs ter Riet and Kessels for attempting to explain the similar sample sizes we found in treatment and control groups. Unfortunately, their suggestion of widespread use of a form of restricted randomization does not shed any new light on our findings. In our original article, we stated, "The strong tendency for the comparison groups to be of equal or similar sizes may be explained by unreported use of (1) restriction, usually blocking...." That explanation includes the model postulated by ter Riet and Kessels, which is just one of many different forms of restriction.Ter Riet and Kessels observe that our "model does not reflect randomized trial conduct in practice." Indeed, that just restates our main argument. The authors of the 96 reports stated or (more usually) implied use of simple, unrestricted randomization. Thereby, they, not we, specified the form of the model used. Furthermore, our approach

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