Received: 18 October 2018
Accepted: 15 April 2019
First Online: 9 May 2019
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board of Seoul National University Hospital with a waiver of informed consent and of its documentation (IRB No: 1504–075-665). Permission to access the de-identified data was granted by the National Health Insurance Service in Korea.
: Not applicable.
: The authors declare that they have no competing interests.
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