1. Haas School of Business, University of California at Berkeley, Berkeley, CA 94720, and NBER (e-mail: )
2. Stanford Institute for Economic Policy Research, Stanford University, 366 Galvez Street, Stanford, CA 94305 (e-mail: )
3. The World Bank, Poverty and Equity Global Practice, 1818 H Street, NW I 4-405, Washington, DC 20433 (e-mail: )