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Kaplan–Meier survival curves of severe acute exacerbation of chronic obstructive pulmonary disease (SAECOPD) are constructed and the log-rank test is used according to SAECOPD in the previous 12 months (p = 0.0001), modified Medical Research Council score (mMRC) (p = 0.003), NYHA (p = 0.01), and COPD assessment test score (CAT) (p = 0.03).
