D Coutinho1, P Sousa2, O Oliveira3, A Rita Gaio4, R Duarte5. 1. Pulmonology Department, Centro Hospitalar de Vila Nova de Gaia/Espinho, Vila Nova de Gaia, Portugal. 2. Faculty of Medicine of Porto University, Porto, Portugal. 3. EPIUnit Institute of Public Health, University of Porto, Porto, Portugal. 4. Centre of Mathematics, University of Porto, Porto, Portugal; Mathematics Department, Faculty of Sciences, University of Porto, Porto, Portugal. 5. Pulmonology Department, Centro Hospitalar de Vila Nova de Gaia/Espinho, Vila Nova de Gaia, Portugal; EPIUnit Institute of Public Health, University of Porto, Porto, Portugal; Chest Disease Centre, Vila Nova de Gaia, Portugal; Department of Clinical Epidemiology, Predictive Medicine and Public Health, University of Porto Medical School, Porto, Portugal. Electronic address: raquel.duarte@chvng.min-saude.pt.