1. Department of Statistics and Population Studies, University of Western Cape, Bellville 7535, South Africa
2. MRC/Wits Rural Public Health and Health Transitions Research Unit, School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg 3193, South Africa
3. Institut de Recherche pour le Développement (IRD), UMI Résiliences, 93140 Bondy, France
4. FERDI, Department of Economics, Université d’Auvergne, 63000 Clermont-Ferrand, France