title: Designed extension of studies based on conditional power.
abstract: We propose a flexible method of extending a study based on conditional power. The possibility for extension when the p value at the planned end is small but not statistically significant is built in to the design of the study. The significance of the treatment difference at the planned end is used to determine the number of additional observations needed and the critical value necessary for use after accruing those additional observations. It may therefore be thought of as a two-stage procedure. Even though the observed treatment difference at stage 1 is used to make decisions, the Type I error rate is protected.
authors.affiliation: Office of Biostatistics Research, National Heart, Lung, and Blood Institute, Bethesda, Maryland 20892, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Proschan
authors.forename: S A
authors.initials: SA
authors.lastname: Hunsberger
mesh_terms: D001699:Biometry / Q000379:methods*; D002792:Cholestyramine Resin / Q000627:therapeutic use; D002986:Clinical Trials as Topic / Q000379:methods* / Q000706:statistics & numerical data; D003327:Coronary Disease / Q000188:drug therapy; D006801:Humans; D015233:Models, Statistical
chemical_list: D002792:Cholestyramine Resin