1 Pulmonology Department, Hospital of Vila Nova de Gaia/Espinho, Vila Nova de Gaia, Portugal. Electronic address: inesfranco_@hotmail.com.
2 Department of Clinical Epidemiology, Predictive Medicine and Public Health, Medical School, University of Porto, Porto, Portugal.
3 Occupational Health and Safety Department, Hospital of Vila Nova de Gaia/Espinho, Vila Nova de Gaia, Portugal.
4 Department of Mathematics, Sciences School, University of Porto, Porto, Portugal.
5 Department of Mathematics, Sciences School, University of Porto, Porto, Portugal; Centre of Mathematics, University of Porto, Porto, Portugal.
6 Pulmonology Department, Hospital of Vila Nova de Gaia/Espinho, Vila Nova de Gaia, Portugal; Department of Clinical Epidemiology, Predictive Medicine and Public Health, Medical School, University of Porto, Porto, Portugal; EPI Unit, Institute of Public Health at University of Porto, Porto, Portugal.