1. Department of Economics, University of Chicago, 11 26 East 59th Street, Chicago, IL 60636, and National Bureau of Economic Research.
2. Department of Economics, University of California, Los Angeles, Bunche Hall 9379, Los Angeles, CA 90095-1477, Federal Reserve Board of Minnesota, and NBER.
3. Research Department, Federal Reserve Bank of Minneapolis, 90 Hennepin Avenue, Box 291, Minneapolis, MN 55480-0291, University of Minnesota, and NBER.