[1] Univ Cape Town, Dept Psychiat & Mental Hlth, Adolescent Hlth Res Unit, POB 814, ZA-7802 Cape Town, South Africa
[2] Univ Cape Town, Adolescent Hlth Res Unit, Div Child & Adolescent Psychiat, Cape Town, South Africa
[3] Univ Bergen, Res Ctr Hlth Promot, Bergen, Norway
[4] MRC, Biostat Unit, Cape Town, South Africa
[5] MRC, Alcohol & Drug Abuse Res Unit, Pretoria, South Africa
[6] Univ Cape Town, Hlth Sci Fac, Sch Publ Hlth & Family Med, Cape Town, South Africa