1. Development Economics Research Group, The World Bank, 1818 H St., NW, MC3–307, Washington, DC 20433.
2. Department of Economics, Yale University, P.O. Box 208269, New Haven, CT 06520–8269 and Innovations for Poverty Action (IPA), The Abdul Latif Jameel Poverty Action Lab (JPAL), and stickK.com.
3. Department of Economics, Dartmouth College, 314 Rockefeller Hall, Hanover, NH 03755 IPA, JPAL, and stickK.com.