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Risk of chronic obstructive pulmonary disease (COPD)-related hospitalization or all-cause mortality associated with Global Initiative for Chronic Obstructive Lung Disease (GOLD) 2011 classification. Curves represent GOLD 2011 group A (A, n = 27), group B (B, n = 91), group C (C, n = 17), and group D (D, n = 191). P = 0.0007 for Kaplan-Meier log-rank test. Subjects at risk are below the x axis.
