Sankhya: The Indian Journal of Statistics

2000, Volume 62, Series B, Pt. 1, 43--69

USING URN MODELS FOR THE DESIGN OF CLINICAL TRIALS

By

A. GREGORY DIRIENZO, Brown University, Providence

SUMMARY. When conducting a clinical trial to compare $K\geq 2$ treatments, it is essential to randomize patients to treatment in order to reduce experimental bias. Typically, an equal number of patients are assigned to each treatment group in order to increase the precision of inference concerning treatment effect. However, if the treatment difference is large and the endpoint potentially fatal, it seems unethical in an unmasked trial to sacrifice a large number of study patients for the purpose of maintaining balance in the number assigned to each treatment group. In this article, we survey those treatment randomization rules that are designed for use in each of the above two experimental situations, and have the empirical advantage of being well explained in terms of an urn model.

AMS (1991) subject classification. Primary: 62L05; Secondary: 60K30.

Key words and phrases. Clinical Trial, randomization, urn design, adaptive biased-coin design, play-the-winner design, response-adaptive design.

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