Optimal response-adaptive designs for normal responses

Most of the available response-adaptive designs in phase III clinical trial set up are not from any optimal consideration. An optimal design for binary responses is given by Rosenberger et al. (2001) and an optimal design for continuous responses is provided by Biswas and Mandal (2004). Recently, Zhang and Rosenberger (2006) [ZR] provided another design for normal responses. Biswas, Bhattacharya and Zhang (2007) pointed out that the design of ZR is not suitable for normally distributed responses, or any distribution having the possibility of negative mean, in general. But they only indicated the problem and bypassed the original problem and set up. In the present paper, we first start with the drawback of ZR. We then provide the appropriate optimal response-adaptive design for normal or continuous distributions which provides the necessary correction for the ZR problem. The proposed methods are illustrated using some real data.