Received: 2 December 2020
Accepted: 19 March 2021
First Online: 7 April 2021
: This study was conducted in accordance with the Declaration of Helsinki and was approved by the institutional review board (IRB) of Seoul National University Hospital (IRB No.E-15-5-079-673). Written consent was waived since every data set of the NHIS-NSC was completely anonymized under strict confidentiality guidelines. Our study was also approved by the National Health Insurance Review Committee (NHIS-2017-2-610).
: Not applicable.
: The authors declare that they have no competing interests.