Received: 15 November 2018
Accepted: 17 May 2019
First Online: 7 June 2019
Ethics approval and consent to participate
: The study was reviewed by the Institutional Review Board (IRB) of Samsung Medical Center (IRB protocol 2015-11-17), and informed consent was exempted because only previously collected de-identified administrative data were used.
: All authors approved the final manuscript in the submitted version and declared themselves in agreement that they agree to all aspects of the work and consent to publication.
: The authors declare that they have no competing interests. The results presented in this article have not been published previously in whole or part, except in abstract format.