1. J. Carlos Escanciano is Assistant Professor, Universidad de Navarra, Facultad de Económicas, Edificio Biblioteca (Entrada Este), Pamplona, 31080, Navarra, Spain . The author thanks Carlos Velasco for many helpful comments and suggestions. The article has also benefited from the comments of two referees, the associate editor, and the joint editor. This research was funded by grants from the Spanish Ministry of Education and Science (SEJ2004-04583/ECON) and by the Universidad de Navarra (16037001).