1. Institute for Life Course Health Research, Department of Global Health, Stellenbosch University, Cape Town 7505, South Africa
2. International Centre for Evidence on Disability, London School of Hygiene and Tropical Medicine, London WC1E 7HT, UK
3. College of Medicine, University of Exeter, Exeter EX4 4QJ, UK
4. Alcohol, Tabaco and Other Drug Research Unit, South African Medical Research Unit, Cape Town 7505, South Africa