Received: 19 September 2019
Accepted: 18 October 2019
First Online: 1 December 2019
Ethics approval and consent to participate
: KNHANES IV-VII are administered by the Korea Center for Disease Control and Prevention (KCDC) and approved by the KCDC Institutional Review Board (2007–02-CON-04-P, 2008-04EXP-01-C, 2009-01CON-03-2C, 2010-02CON-21-C, 2011-02CON-06-C, 2012-01EXP-01-2C, 2013-07CON-03-4C, 2013-12EXP-03-5C, 2015-01-02-6C). Each participant voluntarily participated and provided a signed written consent before participating in the study.
: Not applicable.
: The authors declare that they have no competing interests.