1. Respiratory Division, Department of Internal Medicine, Soonchunhyang University Gumi Hospital, Gumi, Korea.
2. Department of Medicine, Keimyung University Dongsan Hospital, Daegu, Korea.
3. Department of Biostatistic Consulting, Soonchunhyang University Bucheon Hospital, Bucheon, Korea.
4. Department of Occupational and Environmental Medicine, Sungso Hospital, Andong, Korea.