1. University of Chicago, 1126 East 59th Street, Chicago, IL 60637, and NBER (e-mail: )
2. Einaudi Institute for Economics and Finance, EIEF, Via Sallustiana, 62, 00187 Rome, Italy (e-mail: )
3. Harvard Society of Fellows, Department of Economics, Littauer Center 232, Harvard University, Cambridge, MA 02138, and NBER (e-mail: )