1. Department of Statistics and Applied Probability, National University of Singapore, Singapore, Singapore
2. Department of Statistics, University of Washington, Seattle, WA, USA
3. Department of Sociology, University of Washington, Seattle, WA, USA
4. United Nations Population Division, New York, NY, USA
5. MRC/Wits University Rural Public Health and Health Transitions Research Unit (Agincourt), School of Public Health, University of Witwatersrand, Johannesburg, South Africa
6. INDEPTH Network, Durban, South Africa