1 School of Demography, College of Arts and Social Sciences, Australian National University, Acton, ACT, Australia.
2 MRC/Wits Rural Public Health and Health Transitions Research Unit (Agincourt), School of Public Health, University of the Witwatersrand, Johannesburg, South Africa.
3 Institute of Behavioral Science, University of Colorado Boulder, Boulder, CO, USA.
4 Melbourne School of Population and Global Health, University of Melbourne, Melbourne, VIC, Australia.