Optimal two-stage design for a series of pilot trials of new agents

An approach to determine the appropriate sample sizes for a series of scree ning trials to identify promising new therapeutic agents was presented by Y ao, Begg, and Livingston (1996, Biometrics 52, 992-1001). This approach is now improved to a two-stage design that further minimizes the time to ident ify a promising agent under fixed error rates. When applied to data from th e historical experience of exploratory vaccination trials at Memorial Sloan -Kettering Cancer Center, the method demonstrates that relatively small ind ividual screening trials are optimal. The reliability of the results is eva luated using the bootstrap.