[1] Johns Hopkins Univ, Dept Neurol, Sch Med, Baltimore, MD 21287 USA
[2] Johns Hopkins Univ, Dept Med, Sch Med, Baltimore, MD 21287 USA
[3] Johns Hopkins Univ, Dept Biostat, Sch Med, Baltimore, MD 21287 USA
[4] Johns Hopkins Univ, Dept Epidemiol, Sch Med, Baltimore, MD 21287 USA
[5] Johns Hopkins Ctr Hlth Equ, Baltimore, MD USA
[6] NINDS, Stroke Branch, Intramural Res Program, NIH, Bldg 36,Rm 4D04, Bethesda, MD 20892 USA