Received: 4 January 2021
Accepted: 7 June 2021
First Online: 13 July 2021
: The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Review Board (IRB) of Seoul National University (SNU 18-06-062). This study is a de-identified, secondary data analysis study; no consent to participate was necessary. The need for informed consent was waived by the IRB of SNU.
: Not applicable.
: The authors declare that they have no competing interests.