Received: 25 July 2019
Accepted: 27 November 2019
First Online: 5 December 2019
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board of the Korea University Medical Center (IRB No. 2018GR0402). Anonymized and deidentified information for participants was used for analysis, so the requirement for informed consent or parental permission was waived.
: Not applicable.
: The authors declare that they have no competing interests.