- Correspondence to Professor Eun-Cheol Park, Department of Preventive Medicine, College of Medicine, and Institute of Health Services Research, Yonsei University, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 120-752, Republic of Korea;
- Received December 27, 2015
- Revision received February 28, 2016
- Accepted March 5, 2016
- First published April 15, 2016.
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