title: Conditional power for arbitrary survival curves to decide whether to extend a clinical trial.
abstract: This article describes a computer simulation methodology to calculate conditional power for comparing two arbitrary survival curves as an aid in deciding whether or not to extend a clinical trial. The method is a modification of that by Halpern and Brown, which computes unconditional power for comparing arbitrary survival curves at the beginning of a study. The advantage of this method is that it permits conditional power calculations for comparisons of distribution-free survival curves. Power is computed for two commonly used statistical tests, the log-rank test and Gehan's generalization of the Wilcoxon test, and for a modified Kolmogorov-Smirnov test, which is particularly sensitive to crossing survival curves. This method for estimating conditional power should be useful in the situation in which a decision must be made regarding the benefit of continuing a clinical trial. The application of this method is shown using VA Cooperative Study No. 90, "Prognosis and Outcome Following Heart Valve Replacement."
authors.affiliation: VA Cooperative Studies Program Coordinating Center, VA Hospital, Hines, IL 60141.
authors.forename: W G
authors.initials: WG
authors.lastname: Henderson
authors.forename: S G
authors.initials: SG
authors.lastname: Fisher
authors.forename: L
authors.initials: L
authors.lastname: Weber
authors.forename: K E
authors.initials: KE
authors.lastname: Hammermeister
authors.forename: G
authors.initials: G
authors.lastname: Sethi
mesh_terms: D001021:Aortic Valve / Q000601:surgery; D002986:Clinical Trials as Topic / Q000379:methods*; D003198:Computer Simulation; D005500:Follow-Up Studies; D006349:Heart Valve Diseases / Q000601:surgery; D006350:Heart Valve Prosthesis / Q000401:mortality; D006801:Humans; D008432:Mathematical Computing; D008943:Mitral Valve / Q000601:surgery; D011475:Prosthesis Failure; D011897:Random Allocation; D016019:Survival Analysis