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Forrest plot pertaining to the hazard ratios of the time interval to the first episode of severe acute exacerbation of chronic obstructive pulmonary disease (AECOPD) among the patients in the PIFR and control groups, stratified by subgroups. GOLD: Global Initiative for Chronic Obstructive Lung Disease; pMDI: pressurized metered dose inhaler; SMI: soft mist inhaler; DPI: dry powder inhaler.
