1. From the Framingham Heart Study, Framingham, Mass (P.A.S., R.B.D., A.J.B., W.B.K.); the Statistics and Consulting Unit, Department of Mathematics, Boston (Mass) University (P.A.S., R.B.D., A.J.B.); and Section of Preventive Medicine, Department of Medicine, Boston University School of Medicine (W.B.K.).