1. Department of Economics, University of California at Los Angeles, 8283 Bunche Hall, Los Angeles, CA 90095-1477, Institute for the Study of Labor (IZA), and National Bureau of Economic Research.
2. Department of Economics, University of California at Los Angeles, 8283 Bunche Hall, Los Angeles, CA 90095-1477 and IZA.
3. Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30 N-5045, Bergen, Norway, Statistics Norway, and IZA.