[1] Univ N Carolina, Dept Epidemiol, Chapel Hill, NC 27599 USA
[2] Dept Epidemiol, Dept Med, Chapel Hill, NC 27599 USA
[3] Univ Washington, Dept Epidemiol, Seattle, WA 98195 USA
[4] NIH, Bldg 10, Bethesda, MD 20892 USA
[5] Harvard Univ, TH Chan Sch Publ Hlth, Dept Social & Behav Sci, Boston, MA 02138 USA
[6] Univ Mississippi, Dept Med, Med Ctr, Jackson, MS 39216 USA