Modern Approaches to Clinical Trials Using SAS: Classical, Adaptive, and Bayesian Methods

9.3 Restricted Randomization

9.3.1 Permuted Block Randomization

With equal probabilities of assignment, the number of patients in each arm is supposed to be close. Nevertheless, simple randomization typically cannot guarantee a perfect balance across different arms, especially when the sample size is small. By contrast, the restricted randomization aims to achieve an equal number of subjects in each treatment arm, for which two such procedures are introduced below.

The most popular technique for restricted randomization is the so-called permuted block randomization. Considering a sequence of blocks, each block contains a prespecified number of treatment assignments, which are permuted in a random order. For illustration, in a three-arm randomized ...