Received: 13 December 2020
Accepted: 1 February 2021
First Online: 6 February 2021
Ethics approval and consent to participate
: Participants from two different prospective COPD cohort studies in Korea were enrolled: COPD in Dusty Area (CODA) Registry (KCT0000552) and Korean Obstructive Lung Disease Cohort (KOLD). The study design and methods were approved by the Institutional Review Board and informed consent was obtained from each patient of all cohort studies.
: Not required due to study design.
: The authors declare that they have no competing interests.