1. Department of Occupational and Environmental Medicine, International St. Mary's Hospital, Catholic Kwandong University, Incheon, Korea.
2. Department of Occupational Health, Catholic University of Daegu, Daegu, Korea.
3. Department of Statistics, Dongguk University, Seoul, Korea.
4. Department of Occupational & Environmental Medicine, Inha University, Incheon, Korea.
5. Occupational Safety and Health Research Institute, Korea Occupational Safety and Health Agency, Ulsan, Korea.
6. Department of Environmental and Health, Korea National Open University, Seoul, Korea.