1. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, Armed Forces Capital Hospital, Seongnam, Republic of Korea
2. Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine and
3. Department of Internal Medicine, Seoul National University College of Medicine, Seoul, Republic of Korea; and
4. Division of Medical Statistics, Medical Research Collaborating Center, Seoul National University Hospital, Seoul, Republic of Korea
5. Division of Pulmonary and Critical Care Medicine, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Republic of Korea