1. Stanford University, 579 Serra Mall, Stanford, CA 94305 and National Bureau of Economic Research.
2. New York University Stern School of Business, 44 W Fourth Street, New York, NY 10012.
3. Stanford University, 579 Serra Mall, Stanford, CA 94305.
4. London School of Economics, Center for Economic Performance, Houghton Street, London WC2A 2AE.