Received: 24 December 2019
Accepted: 26 June 2020
First Online: 8 July 2020
Ethics approval and consent to participate
: This study used open data from HIRA, which exempted the study from ethical approval according to the Korea National Institute for Bioethics Policy [CitationRef removed]. The Korean bioethics and safety act exempts ethical approval when exploiting existing data. Therefore, this study did not require ethical approval and consent from patients.
: Not applicable.
: The authors declare that they have no competing interests.