Fig. 1. Classiffication or individuals based on smoking and spirometry results.
Flowchart of inclusion of individuals into the study after applying exclusion criteria, and their categorization into four groups based on spirometry (normal spirometry(NS) or abnormal spirometry (AS)) and smoking status (never smoker (NS) or ever smoker ES)). The final four groups used in analysis are Group 1: NS-NS. Normal spirometry and never-smokers: Group 2: NS-ES. Normal spirometry and ever-smokers: Group 3: AS-NS: Normal spirometry and never-smokers and Group 4: AS-ES: Abnormal spirometry and never-smokers.