1. The Institute for Occupational Health, Yonsei University College of Medicine, Seoul, Korea.
2. Department of Preventive Medicine, Yonsei University College of Medicine, Seoul, Korea.
3. Department of Preventive Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.
4. Institute of Occupational & Environmental Medicine, Yonsei University Wonju College of Medicine, Wonju, Korea.