1. From the Departments of Epidemiology (E.B.S., G.H.) and Biostatistics (L.E.C.), School of Public Health, University of North Carolina, Chapel Hill; the Department of Health Evaluation Sciences (D.L.), Pennsylvania State University College of Medicine, Hershey, Pa; and the Department of Public Health Sciences (R.J.W., G.W.E.), Wake Forest University School of Medicine, Winston-Salem, NC.