1Department of Humanities and Social Medicine, Ajou University School of Medicine, Suwon, Korea 
2Department of Occupational and Environmental Medicine, Pusan National University, Yangsan Hospital, Yangsan, Korea 
3Department of Preventive Medicine, College of Medicine, Seoul National University, Seoul, Korea 
4Department of Preventive Medicine, Yonsei University College of Medicine, Seoul, Korea 
5Department of Occupational and Environmental Medicine, Wonju Severance Christian Hospital, Wonju College of Medicine, Yonsei University, Wonju, Korea 
6Department of Preventive Medicine and Institute of Occupational and Environmental Medicine, Wonju College of Medicine, Yonsei University, Wonju, Korea 
© The Author(s). 2016
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