1. Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK, and CAP (e-mail: )
2. Université de Lorraine, 6 rue des Michottes, 54000 Nancy, France, BETA-CNRS, and CREST-ENSAE (e-mail: )
3. Department of Economics, University College London, Drayton House, 30 Gordon Street, London WC1H 0AX, UK, and Sciences Po, Paris (e-mail: )
4. Department of Economics, Sciences Po, 28, rue des Saints Pères, 75007 Paris, France, and UCL (e-mail: )