[1] Johns Hopkins Univ, Dept Neurol, Phipps 446,600 North Wolfe St, Baltimore, MD 21287 USA
[2] Johns Hopkins Univ, Ctr Aging & Hlth, Div Geriatr Med & Gerontol, Baltimore, MD USA
[3] Johns Hopkins Univ, Dept Epidemiol, Baltimore, MD USA
[4] Univ N Carolina, Gillings Sch Global Publ Hlth, Dept Epidemiol, Chapel Hill, NC 27515 USA
[5] Univ Mississippi, Med Ctr, Dept Med, Div Geriatr, Jackson, MS 39216 USA