1. Department of Economics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building E18, Room 269D, Cambridge, MA 02142 (email: )
2. Department of Economics, Universidad de los Andes, Cra 1 No. 18A–12 Bogotá, Of. W 812, Colombia (email: )
3. Harris School of Public Policy, University of Chicago, 1155 E. Sixtieth Street, Chicago, IL 60637 (email: )
4. Department of Economics, Columbia University, 420 West 118th Street, New York, NY 10027 (email: )
5. Department of Economics, Universidad del Rosario, Calle 12C No. 4-69, Oficina 315, Bogotá, Colombia (email: )