title: A sample size adjustment procedure for clinical trials based on conditional power.
abstract: When designing clinical trials, researchers often encounter the uncertainty in the treatment effect or variability assumptions. Hence the sample size calculation at the planning stage of a clinical trial may also be questionable. Adjustment of the sample size during the mid-course of a clinical trial has become a popular strategy lately. In this paper we propose a procedure for calculating additional sample size needed based on conditional power, and adjusting the final-stage critical value to protect the overall type-I error rate. Compared to other previous procedures, the proposed procedure uses the definition of the conditional type-I error directly without appealing to an extra special function for it. It has better flexibility in setting up interim decision rules and the final-stage test is a likelihood ratio test.
authors.affiliation: Organon Inc., 375 Mt Pleasant Ave., West Orange, NJ 07052, USA. G.Li@organoninc.com
authors.forename: Gang
authors.initials: G
authors.lastname: Li
authors.forename: Weichung J
authors.initials: WJ
authors.lastname: Shih
authors.forename: Tailiang
authors.initials: T
authors.lastname: Xie
authors.forename: Jiang
authors.initials: J
authors.lastname: Lu