Funding for this research was provided by:
Ministry of Education (NRF- 2016R1A6A3A11933465)
Ministry of Health and Welfare (HI14C2686)
Received: 12 November 2018
Accepted: 30 May 2019
First Online: 13 June 2019
Ethics approval and consent to participate
: The study was approved by the Ethics Committee of the Korean Center for Disease Control and the Institutional Review Boards of the Korea University Ansan Hospital and the Ajou University School of Medicine. Written informed consent from the participants was obtained prior to each wave of data collection.
: Not applicable.
: The authors declare that they have no competing interests.