Common threads between sample size recalculation and group sequential procedures

Sample size recalculation (SSR) methods ensure that a study closely achieves the required power by allowing for the original sample size to be modified through updating misspecified nuisance parameters. Some SSR procedures extend this concept by incorporating information on the estimated treatment difference as well. While group sequential methodology allows for early stopping of a study in the context of repeated hypothesis tests, SSR usually involves the extension of a study to accommodate misspecified design parameters. This work describes these methods and places them in a common framework. Copyright (C) 2003 John Wiley Sons Ltd.