1. Division of Epidemiology and Global HealthDepartment of Public Health and Clinical Medicine, Umeå Centre for Global Health Research, Umeå University, Umeå, Sweden
2. Institute for Global HealthUniversity College London, London, UK
3. Department of Women's and Children's Health, Uppsala University, Uppsala, Sweden
4. MRC/Wits Rural Public Health and Health Transitions Research UnitSchool of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa