[1] Drexel Univ, Sch Publ Hlth, Dept Epidemiol & Biostat, Philadelphia, PA 19102 USA
[2] Univ Michigan, Sch Publ Hlth, Dept Epidemiol, Ann Arbor, MI 48109 USA
[3] Univ Calif Berkeley, Sch Publ Hlth, Dept Epidemiol, Berkeley, CA 94720 USA
[4] Wake Forest Univ, Bowman Gray Sch Med, Div Publ Hlth Sci, Winston Salem, NC USA
[5] Northwestern Univ, Feinberg Sch Med, Dept Prevent Med, Chicago, IL 60611 USA