[1] Northwestern Univ, Feinberg Sch Med, Dept Prevent Med, Chicago, IL 60611 USA
[2] Univ Calif San Francisco, San Francisco, CA 94143 USA
[3] Brown Univ, Dept Epidemiol, Providence, RI 02912 USA
[4] Univ N Carolina, Carolina Populat Ctr, Chapel Hill, NC USA
[5] Univ Alabama Birmingham, Div Prevent Med, Birmingham, AL USA
[6] Univ Alabama Birmingham, Dept Pediat, Birmingham, AL USA
[7] Harvard Univ, Sch Publ Hlth, Dept Social & Behav Sci, Boston, MA 02115 USA