Daniel Ventosa-santaulària CIDE   Carretera México-Toluca 3655 Col. Lomas de Santa Fe, del. Álvaro Obregón. Mexico D.F., Cd. de México 01210 México   daniel.ventosa@cide.edu             JEL Areas: C1 : Econometric and Statistical Methods: General C2 : Single Equation Models; Single Variables: General