Improved confidence intervals for a binomial parameter following a group sequential phase II clinical trial

Group sequential procedures are widely employed in phase II clinical trials. It is often desirable to provide an interval estimate of the true response rate upon termination of a group sequential phase II clinical trial. The confidence intervals proposed by Jennison and Turnbull (Technometrics 1983; 25: 49-58) are conservative. Utilization of auxiliary statistics based on the overall disease status is proposed to reduce the discreteness of the underlying distribution. Confidence intervals generated by the proposed methods have confidence coefficients closer to the nominal level and have shorter average lengths than JT.