1. Department of Economics, Bendheim Center for Finance, Princeton University, Princeton, New Jersey 08544; Centre for Economic Policy Research, London EC1V 0DX, United Kingdom; and National Bureau of Economic Research, Cambridge, Massachusetts 02138
2. Imperial College London, South Kensington Campus, London SW7 2AZ, United Kingdom
3. MIT Sloan School of Management, Cambridge, Massachusetts 02142; and National Bureau of Economic Research, Cambridge, Massachusetts 02138