[1] Univ Michigan, Sch Med, Stroke Program, Ann Arbor, MI 48109 USA
[2] Univ Pittsburgh, Med Ctr, Stroke Inst, Pittsburgh, PA 15260 USA
[3] Univ Texas, Sch Med, Dept Epidemiol, Houston, TX USA
[4] Univ Texas, Sch Med, Dept Biometry, Houston, TX USA
[5] Univ Texas, Sch Med, Hlth Sci Ctr, Sch Publ Hlth,Stroke Program, Houston, TX USA
[6] Univ Michigan, Sch Publ Hlth, Dept Epidemiol, Ann Arbor, MI 48109 USA