1. From the Epidemiology and Biometry Program, National Heart, Lung, and Blood Institute, Bethesda, Md (A.R.S.); the Departments of Biostatistics (L.E.C.) and Epidemiology (G.H., C.C.P.), University of North Carolina School of Public Health, Chapel Hill; and the Department of Medicine, Baylor College of Medicine, and The Methodist Hospital (W.P.), Houston, Tex.