Received: 2 January 2020
Accepted: 13 April 2020
First Online: 22 April 2020
Ethics approval and consent to participate
: This study used data from the fourth (2007–2009) and sixth (2013–2015) Korean National Health and Nutrition Examination Survey (KNHANES) conducted by the Korea Centers for Disease Control and Prevention (KCDC) that written informed consent was obtained from participants and a parent or guardian for participants under 14 years old. The KCDC acquired ethical approvals from its own Institutional Review Board (IRB) for the KNHANES every year. This study using the KCDC data was exempted from review by the IRB at Gangneung-Wonju National University (GWNUIRB-2016-07).
: Not applicable.
: The authors declare that they have no competing interests.