1. Department of Economics, University of California, Santa Barbara, 2127 North Hall, Santa Barbara, CA 93106, and NBER.
2. Department of Economics, MIT, 50 Memorial Drive, E52-359, Cambridge, MA 02142, Brookings Institution, and NBER.
3. University of Chicago Booth School of Business, 5807 S. Woodlawn Avenue, Chicago, IL 60637, and NBER.