[1] BOWMAN GRAY SCH MED, DEPT PUBL HLTH SCI, WINSTON SALEM, NC USA
[2] UNIV ALBERTA, EPICORE CTR, EDMONTON, AB, CANADA
[3] UNIV WASHINGTON, DEPT BIOSTAT, SEATTLE, WA 98195 USA
[4] UNIV PITTSBURGH, GRAD SCH PUBL HLTH, DEPT EPIDEMIOL, PITTSBURGH, PA USA
[5] UNIV CALIF IRVINE, DEPT MED, ORANGE, CA USA
[6] JOHNS HOPKINS UNIV, SCH MED, DEPT MED, BALTIMORE, MD 21205 USA