[1] Univ Calif San Francisco, Dept Pediat, Div Adolescent & Young Adult Med, San Francisco, CA USA
[2] Univ Toronto, Factor Inwentash Fac Social Work, Toronto, ON, Canada
[3] SRI Int, Ctr Hlth Sci, Biosci Div, Menlo Pk, CA USA
[4] Univ Witwatersrand, Sch Physiol, Dept Physiol, Johannesburg, South Africa
[5] Univ Texas Hlth Sci Ctr Houston, Dept Management Policy & Community Hlth, Houston, TX USA
[6] Johns Hopkins Univ, Johns Hopkins Bloomberg Sch Publ Hlth, Dept Populat Family & Reprod Hlth, Baltimore, MD USA
[7] Univ Southern Calif, Dept Psychiat & Behav Sci, Los Angeles, CA USA
[8] UCSF, Div Adolescent Med, Pediat, Box 0503,550 16th St,Floor 4, San Francisco, CA 94143 USA