1. Department of Agricultural Economics and Economics, Montana State University, Bozeman, Montana 59717;
2. Department of Economics, University of California, Santa Barbara, California 93106;
3. National Bureau of Economic Research, Cambridge, Massachusetts 02138;
4. IZA Institute of Labor Economics, D-53113 Bonn, Germany;
5. LeBow College of Business, Drexel University, Philadelphia, Pennsylvania 19104;
6. Wisconsin School of Business, University of Wisconsin, Madison, Wisconsin 53706