1. Division of Pulmonology, Allergy & Critical Care Medicine, Department of Internal Medicine, Hallym University Medical Center, Seoul, Korea.
2. Department of Pulmonary and Critical Care Medicine and Clinical Research Center for Chronic Obstructive Airway Diseases, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
3. Department of Pulmonary and Critical Care Medicine, Ajou University School of Medicine, Suwon, Korea.
4. Office of Biostatistics, Medical Humanities and Social Medicine, Ajou University School of Medicine, Seoul, Korea.
5. Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
6. Department of Internal Medicine, Konkuk University School of Medicine, Seoul, Korea.
7. Department of Internal Medicine, CHA Bundang Medical Center, CHA University, Seongnam, Korea.
8. Division of Pulmonology, Department of Internal Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, Korea.
9. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea.
10. Department of Internal Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, Korea.
11. Department of Internal Medicine, Seoul St. Mary's Hospital, Catholic University of Korea, Seoul, Korea.
12. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, College of Medicine, Chungbuk National University, Cheongju, Korea.