1. The World Bank, 1818 H St. NW Washington, DC 20433 (e-mail: )
2. Paris School of Economics, 48 boulevard Jourdan, 75014 Paris, France and Abdul Latif Jameel Poverty Action Lab (JPAL) (e-mail: )
3. Department of Economics, Massachusetts Institute of Technology (MIT), 50 Memorial Drive, Cambridge MA 02142 and National Bureau of Economics (NBER) (e-mail: )
4. Stanford Department of Economics, 579 Serra Mall, Stanford CA 94305 and NBER (e-mail: )
5. Paris School of Economics 48 boulevard Jourdan, 75014 Paris, France and JPAL (e-mail: )