1 Department of Medical Epidemiology, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy.
2 Department of Public Health, Experimental and Forensic Medicine, University of Pavia, Pavia, Italy.
3 Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy.
4 Faculty Health, Medicine and Life Sciences, Department of Epidemiology, Maastricht University, Maastricht, The Netherlands.
5 Department of Medical Epidemiology, Istituto di Ricerche Farmacologiche Mario Negri IRCCS, Milan, Italy. Electronic address: silvano.gallus@marionegri.it.