Funding for this research was provided by:
National Health Insurance Service (NHIS-1579, NHIS-1579, NHIS-1579, NHIS-1579, NHIS-1579)
Received: 13 February 2018
Accepted: 11 February 2019
First Online: 18 February 2019
Ethics approval and consent to participate
: This study was approved by the Institutional Review Board (IRB) of Severance Hospital, Seoul, South Korea (IRB approval number: Y–2017-0013). As this was a retrospective study, the IRB waived the requirement for informed consent.
: Not applicable.
: The authors declare that they have no competing interests.
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