1. Department of Economics, MIT, 50 Memorial Drive, E52-371, Cambridge, MA 02142, and NBER.
2. CEMFI, Casado del Alisal 5, 28014 Madrid, Spain.
3. School of International Relations and Pacific Studies, 0519, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0519, and NBER.