From the Department of Neurology (S.E.K., J.A.C., J.M.L., B.L.C., E.C.R., M.L.M., M.B.C.) and Center for Clinical Epidemiology and Biostatistics, Department of Biostatistics and Epidemiology (A.R.L.), University of Pennsylvania Medical Center, Philadelphia, Pa. (1999-08時点)