1. The World Bank, 1818 H Street, NW, Washington, DC 20433.
2. Department of Economics, University of California–Berkeley, 621 Evans Hall, Berkeley, CA 94720, and School of Economics and Management, Tsinghua University.
3. Department of Economics, University of California-Berkeley, 549 Evans Hall #3880, Berkeley, CA 94720-3880, and CEPR.
4. CEFIR, Moscow 117418, Russia, and CEPR.