Constrained randomization in a therapeutic efficacy trial.

The use of valid constrained randomization is presented for a therapeutic efficacy trial. The construction and evaluation of randomization schemes are studied for two treatment replicates per block and for hypothesized linear gradients. Two different isomorphism classes of designs are compared using the variance of the mean squared error criterion. The results indicate that valid constrained randomization schemes can be constructed that are superior to ordinary randomization. A mastitis efficacy trial provided the specific problem to be solved.