1. Department of Occupational and Environmental Medicine, Ewha Womans University Seoul Hospital , Seoul, Republic of Korea
2. Department of Social and Preventive Medicine, Hallym University College of Medicine , Chuncheon, Republic of Korea
3. Institute of Social Medicine, Hallym University College of Medicine , Chuncheon, Republic of Korea
4. Department of Occupational and Environmental Medicine, College of Medicine, The Catholic University of Korea , Seoul, Republic of Korea