1 Centre for Health Economics, University of York, Heslington, YO10 5DD York, United Kingdom.
2 Toulouse School of Economics, University of Toulouse Capitole, 21 allée de Brienne, F-31015 Toulouse Cedex 6, France.
3 Department of Economics and Related Studies, University of York, Heslington, YO10 5DD York, United Kingdom. Electronic address: luigi.siciliani@york.ac.uk.