1. Northwestern University; Searle Center for Law, Regulation and Economic Growth; Chicago Illinois 60611 U.S.A.
2. Institut d'Economia de Barcelona; Facultat d'Economia i Empresa, UB c/Tinent Coronel Valenzuela, 1-11; 08304 Bellaterra Barcelona Spain
3. Maastricht University; UNU-MERIT; Maastricht The Netherlands