1. Gies College of Business, University of Illinois, Champaign, IL 61820
2. National Bureau of Economic Research, Cambridge, MA 02138
3. Department of Resource Economics, University of Massachusetts, Amherst, MA 01003
4. Department of Economics, Monash University, Caulfield East, VIC 3145, Australia
5. IZA Institute of Labor Economics, 53113 Bonn, Germany