1. Group Health Research Institute; University of Washington School of Public Health, Seattle, WA; National Cancer Institute, Bethesda, MD; Kaiser Permanente, Denver, CO, Portland, OR, and Honolulu, HI; Geisinger Health System, Danville, PA; Health Services Research Division, LCF Research, Albuquerque, NM; Harvard Medical School and Harvard Pilgrim HealthCare Institute; and Harvard Vanguard Medical Associates, Boston, MA