1. Department of Economics, University of Chicago, 1126 East 59th Street, Chicago, IL 60637, Universidad Torcuato di Tella (Argentina), and NBER.
2. Department of Economics, University of Chicago, 1126 East 59th Street, Chicago, IL 60637, and Federal Reserve Bank of Minneapolis.
3. Research Department, Federal Reserve Bank of Minneapolis, P.O. Box 291, Minneapolis, MN 55480-0291.