Study flow chart and subject classifications. Normal lung function was defined by FEV1/FVC ≥ 70% and %FEV1 ≥ 80% and %FVC ≥ 80%, by both pre- and post-salbutamol tests. Pre-salbutamol values were used to classify normal lung function if post-salbutamol test was not done. Abnormal lung function was defined by either FEV1/FVC < 70% or %FEV1 < 80% or %FVC < 80%, either pre- or post-salbutamol test. Symptomatic was defined as having cough, sputum or breathlessness. Obstructive lung function was classified as pre-salbutamol FEV1/FVC < 70% without post-salbutamol values. COPD was defined as post-salbutamol FEV1/FVC < 70%. Restrictive lung function was defined by FEV1/FVC ≥ 70% and %FVC < 80%, either before or after salbutamol inhalation. Asthma was defined as reversible FEV1, which improved more than 12% and 200 ml after salbutamol inhalation.