1. Nossal Institute for Global Health, Melbourne School of Population and Global Health, University of Melbourne , Melbourne, VIC, Australia
2. School of Demography, Research School of Social Sciences, Australian National University , Canberra, ACT, Australia
3. MRC/Wits Rural Public Health and Health Transitions Research Unit (Agincourt), School of Public Health, Faculty of Health Sciences, University of the Witwatersrand , Johannesburg, Gauteng, South Africa