a package for creating, monitoring and modifying a group sequential design
The DESCRIPTION file: DESCRIPTION
David A Schoenfeld, PhD and Hui Zheng, PhD
Proschan, MA, Lan, KKG, Wittes, JT, Statistical Monitoring of Clinical Trials: A Unified Approach, Springer, 2006
Schoenfeld DA, "A Simple Algorithm for Designing Group Sequential Clinical Trials", Biometrics. 2001 Sep;57(3):972-4.