1. Department of Economics, University of Regensburg, D-93040 Regensburg, Germany.
2. Institute for Empirical Research in Economics, University of Zurich, Blümlisalpstrasse 10, CH-8006 Zurich, Switzerland.
3. Department of Economics, University of Linz, Altenberger Strasse 69, A-4040 Linz, Austria, and Centre for Economic Policy Research (London).