1. Unit of Biostatistics, Epidemiology, and Public Health, Department of Statistics and Quantitative Methods; University of Milano-Bicocca; Milan Italy
2. Division of Pneumology; “Guido Salvini” Hospital; Garbagnate Milanese Italy
3. Unit of Epidemiology and Medical Statistics; University of Verona; Verona Italy
4. Department of Health Science; University of Milano-Bicocca; Milan Italy
5. Respiratory Unit; “San Gerardo” Hospital; Monza Italy
6. Operative Unit of Territorial Health Services; Lombardy Region; Milan Italy