1. Institute for Empirical Research in Economics, University of Zurich, Blümlisalpstrasse 10, 8006 Zurich.
2. Institute for the Study of Labor (IZA), Schaumburg-Lippe-Str. 7/9, 53113 Bonn, Germany.
3. Federal Reserve Bank of Boston, 600 Atlantic Avenue, Boston, MA 02210.