[1] Johns Hopkins Univ, Sch Med, Dept Med, Baltimore, MD 21205 USA
[2] Johns Hopkins Univ, Sch Hyg & Publ Hlth, Dept Epidemiol, Baltimore, MD USA
[3] ARIC Ultrasound Reading Ctr, Bowman Gray Sch Med, Dept Neurol, Winston Salem, NC USA
[4] NHLBI, Bethesda, MD 20892 USA
[5] Univ N Carolina, ARIC Data Coordinating Ctr, Chapel Hill, NC 27515 USA