1. Department of Economics and Finance, University of Rome Tor Vergata, Via Columbia 2, Rome, I-00133, Italy
2. Nottingham School of Economics, Sir Clive Granger Building, University Park, Nottingham, NG7 2RD, UK; University of Rome Tor Vergata, Department of Economics and Finance, Via Columbia 2, I-00133, Rome, Italy; and C.E.P.R, 90-98 Goswell Street, London, EC1V 7DB, UK
3. University of Siena, Department of Economics and Statistics, Piazza San Francesco 7, Siena, I-53100, Italy