1. Sloan School of Management, Massachusetts Institute of Technology, 100 Main Street, Cambridge, MA 02142 (e-mail: )
2. Department of Economics, Harvard University 1805 Cambridge Street, Cambridge, MA 02138 and National Bureau of Economic Research (NBER) (e-mail: )
3. National Bank of Belgium, European Center for Advanced Research in Economics and Statistics (ECARES), Universite Libre de Bruxelles, Av. F.D. Roosevelt, 50, CP 114/04, 1050 Brussels, Belgium and Center for Economic and Policy Research (CEPR) (e-mail: )
4. Cox School of Business, Southern Methodist University; 6212 Bishop Blvd, Dallas, TX 75275 (e-mail: )
5. Sloan School of Management, Massachusetts Institute of Technology 100 Main Street, Cambridge, MA 02142, and NBER (e-mail: )