1. Department of Economics, Boston College, 140 Commonwealth Avenue, Chestnut Hill, MA 02467-3806, and National Bureau of Economic Research.
2. Economic Research MS 1130, Federal Reserve Bank of San Francisco, 101 Market Street, San Francisco, CA 94105.
3. Department of Economics, University of Michigan, 611 Tappan Street, Ann Arbor, MI 41809-1220, and NBER.