[1] Univ Oklahoma, Hlth Sci Ctr, Ctr Amer Indian Hlth Res, Oklahoma City, OK 73190 USA
[2] Univ Oklahoma, Hlth Sci Ctr, Dept Biostat & Epidemiol, Oklahoma City, OK 73190 USA
[3] Univ N Carolina, Dept Epidemiol, Chapel Hill, NC USA
[4] Univ Oklahoma, Hlth Sci Ctr, Dept Obstet & Gynecol, Oklahoma City, OK 73190 USA
[5] MedStar Res Inst, Washington, DC USA