1. From the Division of Epidemiology (A.R.F.), School of Public Health, University of Minnesota, Minneapolis; the Division of Hematology (N.A., H.J., K.K.W.), University of Texas Medical School, Houston; the Biostatistics Department (E.P.), University of North Carolina, Collaborative Studies Coordinating Center, Chapel Hill; and the KTL-National Public Health Institute (V.S.), Department of Epidemiology, Helsinki, Finland.