Statistics
Nonparametric tests were used due to asymmetric distribution in most variables. Mann-Whitney U test was used for comparison between two groups and Chi2-test or Fisher’s exact test (when at least one cell had an expected count less than five) were used to explore relationships between categorical variables. Change in lung function variables before versus after bronchodilator were evaluated by Wilcoxon signed rank test or McNemar’s test. P-values <0.05 were considered significant.