1. Paris School of Economics and JPAL, 48 Boulevard Jourdan, 75014 Paris, France.
2. Massachusetts Institute of Technology and NBER, Department of Economics, 50 Memorial Drive, Cambridge, MA 02142.
3. Stanford and NBER, Department of Economics, 579 Serra Mall, Stanford, CA 94305.
4. UC Louvain, Institut de Recherche Économique et Sociale, Place Montesquieu 3, B-1348 Louvain-la-Neuve, Belgium.
5. Massachusetts Institute of Technology, Department of Economics, 50 Memorial Drive Cambridge, MA 02142.