1. Department of Mathematics and Statistics University of North Carolina at Charlotte Charlotte NC 28223 U.S.A
2. Department of Mathematics and Statistics University of North Florida Jacksonville FL 32224 U.S.A
3. CBER, Food and Drug Administration Silver Spring MD 20993 U.S.A
4. Department of Biostatistics University of Washington Seattle WA 98195 U.S.A
5. Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center Seattle WA 98109 U.S.A