1. Harvard-MIT Center for Regulatory Science, Harvard Medical School, 210 Longwood Av, Boston, MA, USA
2. Dept. of Business and Economics, Universitat Pompeu Fabra, Carrer de Ramon Trias Fargas, 25-27, 08005 Barcelona, Spain
3. Dept. of Statistics, University of Warwick, Coventry CV4 7AL, UK