1. From the Framingham Heart Study, Framingham, Mass (C.S.P.L., W.L., E.J.B., R.S.V.); Department of Biostatistics, Boston University School of Public Health, Boston, Mass (V.X., L.M.S.); Mayo Clinic, Rochester, Minn (C.S.P.L., M.M.R.); Veterans Administration Hospital, West Roxbury, Mass (J.A.); Cardiovascular Engineering Inc, Norwood, Mass (G.F.M.); and Preventive Medicine and Cardiology Sections, Boston University School of Medicine, Boston, Mass (E.J.B., R.S.V.).