1. From the Division of Cerebrovascular Diseases (P.H.D.), Department of Neurology, Division of Biostatistics (J.D.D., L.T.M., R.M.L.), Department of Preventive Medicine and Environmental Health, and Division of Pediatric Cardiology (L.T.M., R.M.L.), Department of Pediatrics, University of Iowa College of Medicine, Iowa City, Iowa.