1. Department of Occupational and Environmental Medicine, Seoul St. Mary’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea.
2. Department of Occupational and Environmental Medicine, Inha University Hospital, Inha University, Incheon, Korea.
3. Department of Economics, Sungkyunkwan University, Seoul, Korea.
4. Department of Human Systems Medicine, Seoul National University College of Medicine, Seoul, Korea.