Some recent developments in the design of adaptive clinical trials

For clinical trials that compare two or more competing treatments, the literature proposes several randomizat ion rules that aim at favouring, at each stage of the trial, the treatment that appears to be best. In two papers the present authors have suggested criteria of optimal allocation that combine inferential precision and ethical gain by means of flexible weights, in order to achieve a good trade-off between efficiency and ethical concerns. The ensuing optimal allocation of the treatments can be targeted by a suitable response-adaptive randomization rule. The purpose of this paper is to illustrate and extend the results previously obtained by the authors to a wider range of statistical models for comparative trials. Methods for implementing these designs are given. Some numerical examples are included in order to enhance the applicability.