1. From the Department of Biostatistics (A.L.D., J.L.), Boston University School of Public Health, Mass; the Departments of Neurology (A.L.D.) and Epidemiology and Preventive Medicine (M.G.L., E.J.B., R.S.V., D.L.), Cardiology Section (E.J.B., R.S.V., D.L.), Boston University School of Medicine, Mass; the National Heart, Lung, and Blood Institute’s Framingham Heart Study (M.G.L., E.J.B., R.S.V., D.C., D.L.), Framingham, Mass; and Cardiovascular Engineering, Inc. (G.F.M.), Holliston, Mass.