1. Department of Statistics; University of British Columbia; 333-6356 Agricultural Road Vancouver B.C. V6T 1Z2 Canada
2. Department of Environmental and Occupational Health, School of Public Health; Drexel University; 1505 Race Street, Room 1332 Philadelphia PA 19102 U.S.A.
3. Department of Epidemiology, School of Public Health; University of North Carolina; 170 Rosenau Hall, CB #7400, 135 Dauer Drive, Chapel Hill NC 27599 U.S.A.