Received: 6 March 2018
Accepted: 10 September 2018
First Online: 15 September 2018
Ethics approval and consent to participate
: KNHANES VI is administered by the Korea Center for Disease Control and Prevention (KCDC) and approved by the KCDC Institutional Review Board (2013-07CON-03-4C, 2013-12EXP-03-5C and 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.
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