1. Institute for Empirical Research in Economics, University of Zurich, Blümlisalpstrasse 10, CH-8006 Zürich.
2. Department of Economics, Harvard University, Littauer Center 220, 1805 Cambridge Street, Cambridge, MA 02138.
3. Faculty of Business and Economics, University of Lausanne, Quartier UNIL-Dorigny, Internef 612, CH-1015 Lausanne.