1. Sequential Medical Trials;Armitage,1975
2. Group sequential methods in the design and analysis of clinical trials;Pocock;Biometrika,1977
3. The Design and Analysis of Sequential Clinical Trial;Whitehead,1991
4. Exact confidence intervals following a group sequential test;Tsiatis;Biometrics,1984
5. Discrete sequential boundaries for clinical trials;Lan;Biometrika,1983