[1] Univ Oxford, Dept Social Policy & Intervent, Oxford, England
[2] Univ Oxford, Nuffield Coll, Oxford, England
[3] Univ Cape Town, Ctr Social Sci Res, Cape Town, South Africa
[4] Univ Cape Town, Dept Sociol, Cape Town, South Africa
[5] Ludwig Maximilians Univ Munchen, Inst Med Informat Proc Biometry & Epidemiol, Munich, Germany
[6] Univ Cape Town, Dept Psychiat & Mental Hlth, Cape Town, South Africa
[7] Dept Social Policy & Intervent, Barnet House,32-37 Wellington Sq, Oxford OX12ER, England