1. Alcohol, Tobacco and Other Drug Research Unit, South African Medical Research Council, Cape Town, South Africa
2. School of Public Health, University of Cape Town, Cape Town, South Africa
3. Biostatistics Unit, South African Medical Research Council, Cape Town, South Africa
4. Department of Psychiatry, Stellenbosch University, Cape Town, South Africa
5. Department of Psychiatry and Mental Health, University of Cape Town, Cape Town, South Africa