1. Department of Economics, University of California, Berkeley, California 94708;
2. Department of Economics, University of Maastricht, 6211 TC Maastricht, The Netherlands
3. National Bureau of Economic Research, Cambridge, Massachusetts 02138
4. Institute for Fiscal Studies, WC1E 7AE London, United Kingdom
5. INNO-tec, Ludwig-Maximilians-Universität München, D-80539 München, Germany;
6. Centre for Economic Policy Research, EC1V 3PZ London, United Kingdom