Funding for this research was provided by:
National Research Foundation of Korea (NRF-2016R1C1B1009088)
Received: 20 February 2019
Accepted: 10 June 2019
First Online: 18 June 2019
Ethics approval and consent to participate
: The study was approved by the local ethics committees in each participating hospital, and informed consent was waived.
: Not applicable.
: The authors declare that they have no competing interests.