1. Department of Psychiatry and Mental Health, and Adolescent Health Research Institute, University of Cape Town. P.O. Box 240, Plumstead, 7801, South Africa
2. Department of Psychiatry and Mental Health, and Adolescent Health Research Institute, University of Cape Town, South Africa
3. Biostatistics Unit, South African Medical Research Council, and Community Health Department, University of the Free State, Bloemfontein, South Africa
4. Biostatistics Unit, South African Medical Research Council, South Africa
5. Department of Biobehavioral Health, The Pennsylvania State University, United States of America