1. School of Economics, University of Bristol, Bristol BS8 1TU, United Kingdom
2. Erasmus School of Economics, Erasmus University Rotterdam, Rotterdam 3062, Netherlands
3. National Population Commission, Abuja P.M.B. 281, Nigeria
4. Institute for Global Health, University College London, London WC1N 1EH, United Kingdom
5. Department of Economics, University College London, London WC1H 0AN, United Kingdom
6. Institute for Fiscal Studies, London WC1E 7AE, United Kingdom
7. Cemmap, London WC1E 7AE, United Kingdom
8. Department of Health Policy, Stanford Medical School, Stanford, CA 94305
9. National Bureau of Economic Research, Cambridge, MA 02138-5398