1. From the Statistics and Consulting Unit (M.F.E., R.B.D.), Department of Mathematics and Statistics, Boston University, Mass; the Department of Biostatistics (L.M.S.), Boston University School of Public Health, Mass; the Department of Psychology (M.F.E., P.K.E.), University of Maine, Orono; and the Departments of Neurology (P.A.W., S.S., R.A.), Preventive Medicine (E.J.B., R.S.V.), and Cardiology (E.J.B., R.S.V.), Boston, Mass.