1. Alcohol & Drug Abuse Research Unit, South African Medical Research Council, South Africa
2. Alcohol & Drug Abuse Research Unit, South African Medical Research Council, South Africa; School of Public Health, University of the Witwatersrand, Johannesburg, South Africa
3. Alcohol & Drug Abuse Research Unit, South African Medical Research Council, South Africa; Department of Psychiatry & Mental Health, University of Cape Town, South Africa
4. Health Systems Research Unit, South African Medical Research Council, South Africa
5. Biostatistics Unit, South African Medical Research Council, South Africa