Department of Public Health, Kurume University School of Medicine, Kurume, Japan
Copyright © 2018 The Korean Society for Preventive Medicine
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
CONFLICT OF INTEREST
The authors have no conflicts of interest associated with the material presented in this paper.