1. Research Centre for Education and the Labour Market (ROA), Maastricht University; School of Business and Economics; P. O. Box 616 6200 MD Maastricht The Netherlands
2. Department of Agricultural Economics; Purdue University; West Lafayette IN USA
3. Department of Spatial Economics; Vrije Universiteit Amsterdam; De Boelelaan 1105 1081 HV Amsterdam The Netherlands
4. Tinbergen Institute; Amsterdam The Netherlands