1. Department of Spatial Economics, Faculty of Economics and Business Administration, VU University Amsterdam, De Boelelaan 1105, 1081 HV, Amsterdam, The Netherlands
2. Institute for Social and Economic Research, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, England
3. Department of Economics, Faculty of Statistics, University of Bologna, Piazza Scaravilli 2, 40126 Bologna, Italy