Received: 9 November 2017
Accepted: 28 June 2018
First Online: 5 July 2018
Ethics approval and consent to participate
: The KNHANES surveys (ExternalRef removed/) are approved by the Korean Center for Disease Control (2010-02CON-21-C, 2011-02CON-06-C, 2012-01EXP-01-2C, 2013-07CON-03-4C, 2013-122EXP-03-5C, and 2015–01-02-6C), and all participants provide written informed consent.
: Not applicable.
: The authors declare that they have no competing interests.
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