title: A SAS macro for sample size re-estimation.
abstract: The assessment of sample size in clinical trials comparing means requires a variance estimate of the main efficacy variable. If no reliable information about the variance of the key response is available at the beginning of a clinical trial, the use of data from the first 'few' patients entered in the trial ('internal pilot') may be appropriate to estimate the variance and thus to recalculate the required sample size. A SAS macro that implements the EM algorithm for carrying out and simulating such interim power evaluations without unblinding the treatment status is presented.
authors.affiliation: Division of Nephrology, Medical Department, University of Ulm, Ulm, Germany. dzellner@t-online.de
authors.forename: D
authors.initials: D
authors.lastname: Zellner
authors.forename: G E
authors.initials: GE
authors.lastname: Zellner
authors.forename: F
authors.initials: F
authors.lastname: Keller
mesh_terms: D000465:Algorithms; D002986:Clinical Trials as Topic / Q000706:statistics & numerical data*; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000706:statistics & numerical data; D018401:Sample Size; D012984:Software