1. Department of Preventive Medicine, College of Medicine Yonsei University Seoul Korea
2. Institute of Health Services Research, College of Medicine Yonsei University Seoul Korea
3. Department of Public Health, Graduate School Yonsei University Seoul Korea
4. Department of Dermatology, Severance hospital, College of medicine Yonsei University Seoul Korea
5. The Institute for Occupational Health Yonsei University College of Medicine Seoul Korea