Table 2. Comparison between total dataset and PSM dataset.

Data represented as mean±standard deviation or number (%). P-value by independent student t-test (continuous variables) or χ² test (categorical vari-ables).

^a)P<0.05. ^b)P<0.01.

PSM, propensity score matching; BMI, body mass index; COPD, chronic obstructive pulmonary disease.