Funding for this research was provided by:
National Research Foundation of Korea (NRF-2012R1A1A3008042, NRF-2018M3C7A1056898, NRF-2016R1E1A1A01943303)
Text and Data Mining valid from 2019-05-17
Received: 14 November 2018
Accepted: 15 April 2019
First Online: 17 May 2019
Compliance with ethical standards
: All procedures involving human participants were performed in accordance with the ethical standards of the institutional research committee and with the principles of the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. Formal consent is not required for this type of study.
: The Institutional Review Board of our university approved this retrospective study, and the requirement to obtain informed consent was waived.