First Author:   Francisco Sanchez-Sanchez CIMAT sanfco@cimat.mx   Jalisco S/N, Mineral de Valenciana Guanajuato, 36240, Mexico   52 473 732 7155(Phone) 52 473 732 7155(Fax) Second Author: Ruben Juarez Rice University ruben@rice.edu   Department of Economics, Rice University, 6100 Main St Houston, 77005, USA       Third Author: Luis Hernandez-Lamoneda CIMAT lamoneda@cimat.mx   Jalisco S/N, Mineral de Valenciana Guanajuato, 36240, Mexico   52 473 732 7155(Phone) 52 473 732 5749(Fax) http://www.cimat.mx