1. MRC/Wits Rural Public Health and Health Transitions Research Unit (Agincourt)School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
2. Umeå Centre for Global Health Research, Epidemiology and Global Health Unit, Department of Public Health and Clinical Medicine, Umeå University, Umeå, Sweden
3. INDEPTH NetworkAccra, Ghana
4. F. Hoffmann-La Roche AG, Basel, Switzerland
5. MRC/Wits Developmental Pathways for Health Research UnitDepartment of Paediatrics, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa