1Cancer Prevention and Control Unit, Institut Català d'Oncologia2Department of Public Health, Universitat de Barcelona, 08907 L'Hospitalet, Spain3Istituto di Ricerche Farmacologiche “Mario Negri”, 20157 Milan, Italy4Department of Economy, Centre de Recerca en Economia de la Salut, Universitat Pompeu Fabra, 08003 Barcelona, Spain5Istituto di Biometria e Statistica Medica, Universita degli Studi di Milano, 20133 Milan, Italy6Departament of Epidemiology and Hygiene, School of Medicine, Universidade do Porto, Porto, Portugal7London School of Hygiene and Tropical Medicine, London University, London WC1E 7HT, UK