[1] KAISER PERMANENTE MED CARE PROGRAM, DIV RES, OAKLAND, CA USA
[2] UNIV MINNESOTA, SCH PUBL HLTH, DIV EPIDEMIOL, MINNEAPOLIS, MN 55455 USA
[3] UNIV ALABAMA, SCH PUBL HLTH, DEPT EPIDEMIOL, BIRMINGHAM, AL 35233 USA
[4] UNIV WASHINGTON, SCH MED, DEPT MED, SEATTLE, WA 98195 USA
[5] UNIV WASHINGTON, SCH MED, DEPT PATHOL, SEATTLE, WA 98195 USA
[6] UNIV CALIF SAN FRANCISCO, DEPT EPIDEMIOL & INT HLTH, SAN FRANCISCO, CA 94143 USA