1. Department of Economics and Statistics; Via Giovanni Paolo II 84084 Fisciano (SA) Italy
2. Health Econometrics Data Group; University of York; Heslington, York, YO10 5DD UK
3. Rheinisch Wesffälisches Institut für Wirtschaftsforschung; Department of “Health Economics”; Hohenzollernstraße 1-3, D-45128 Essen Germany