1 Cancer Epidemiology Unit, Department of Medical Sciences, University of Turin and CPO-Piemonte, Turin, Italy, Centre for Statistical Methodology, London School of Hygiene and Tropical Medicine, London, UK, Departments of Medical Statistics and Non-communicable Disease Epidemiology, Faculty of Epidemiology and Population Health, London School of Hygiene and Tropical Medicine, London, UK and Centre for Public Health Research, Massey University, Wellington, New Zealand.