1. Emeritus Professor of Medical Demography, Department of Population Health; London School of Hygiene & Tropical Medicine; Keppel Street London WC1E 7HT United Kingdom
2. Doctoral student, Faculty of Epidemiology and Population Health, Department of Population Health; London School of Hygiene & Tropical Medicine; Keppel Street London WC1E 7HT United Kingdom
3. Principal Research Scientist, Department of Global Health and Population; Harvard T.H. Chan School of Public Health; Boston Massachusetts