First Author:   Nicola Branzoli University of Wisconsin Madison branzoli@wisc.edu   William H. Sewell Social Science Building, 1180 Observatory Drive, 53706-1393 Madison, 53706-1393, U.S.A.       Second Author: Guido Ascari University of Pavia, Department of Economics guido.ascari@unipv.it   Via S. Felice 5 Pavia, 27100, Italy   +39 0382 986211(Phone) +39 0382 304226(Fax) http://economia.unipv.it/pagp/pagine_personali/gascari/ascari.htm#an1