1. Department of Applied Mathematics; Hong Kong Polytechnic University; Hong Kong China
2. Biostatistics and Bioinformatics Branch; Eunice Kennedy Shriver National Institute of Child Health and Human Development; Rockville MD 20852 U.S.A.
3. Center for Biologics Evaluation and Research; Food and Drug Administration; Rockville MD 20852 U.S.A.
4. Center for Drug Development and Research; Food and Drug Administration; Silver Spring MD 20993 U.S.A.
5. Department of Biostatistics and Bioinformatics; Duke University Medical Center; Durham NC 27708 U.S.A.