[1] NHLBI, Div Epidemiol & Clin Applicat, Bethesda, MD 20982 USA
[2] Univ Minnesota, Sch Publ Hlth, Div Epidemiol, Minneapolis, MN 55455 USA
[3] Univ N Carolina, Collaborat Studies Coordinating Ctr, Chapel Hill, NC USA
[4] Univ Mississippi, Med Ctr, Div Epidemiol, Jackson, MS 39216 USA