1. Tuck School of Business at Dartmouth and NBER, 100 Tuck Hall, Hanover, NH 03755.
2. Georgetown University and NBER, 521 Hariri, McDonough School of Business, Washington, DC 20057.
3. London School of Economics and CEPR, Houghton Street, London WC2A 2AE UK.
4. Yale School of Management and NBER, 135 Prospect Street, New Haven, CT 06520.