title: Some Issues of Sample Size Calculation for Time-to-Event Endpoints Using the Freedman and Schoenfeld Formulas.
abstract: This article deals with seven special issues related to the assumptions, applicability, and practical use of formulas for calculating power or sample size, respectively, for comparative clinical trials with time-to-event endpoints, with particular focus on the well-known Freedman and Schoenfeld methods. All problems addressed are illustrated by numerical examples, and recommendations are given on how to deal with them in the planning of clinical trials.
authors: a National Center for Tumor Diseases Heidelberg , Heidelberg , Germany.
authors: Ulrich R
authors: UR
authors: Abel
authors: b Institute of Medical Biometry and Informatics, University of Heidelberg , Heidelberg , Germany.
authors: Katrin
authors: K
authors: Jensen
authors: a National Center for Tumor Diseases Heidelberg , Heidelberg , Germany.
authors: Irini
authors: I
authors: Karapanagiotou-Schenkel
authors: b Institute of Medical Biometry and Informatics, University of Heidelberg , Heidelberg , Germany.
authors: Meinhard
authors: M
authors: Kieser
mesh_terms: D000465:Algorithms; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data; D003198:Computer Simulation; D023381:Endpoint Determination / Q000706:statistics & numerical data*; D006801:Humans; D015233:Models, Statistical; D011336:Probability; D012107:Research Design; D018401:Sample Size; D016019:Survival Analysis; D016896:Treatment Outcome
keywords: Controlled clinical trial; Freedman formula; Sample size; Schoenfeld formula; Time-to-event data