Sample size considerations - boundary.exe is a program for computing sequential boundaries, as descibed in the paper "A Simple Algorithm for Designing Group Sequential Clinical Trials" (Schoenfeld, Biometrics 57, 972-974; September 2001). The program was implemented in Matlab and runs as a batch job from a DOS command prompt.
Dr. Schoenfeld's Biosketch - Dr. Schoenfeld's NIH biosketch in pdf format
MGH Biostatistics - Web Site for Biostatistics Unit at Massachusetts General Hospital