¹Department of Internal Medicine and ²Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, CHA Bundang Medical Center, CHA University, Seongnam, ³Division of Pulmonology, Department of Internal Medicine, Hanyang University Guri Hospital, Hanyang University College of Medicine, Guri, ⁴Department of Internal Medicine, Kangwon National University College of Medicine, Chuncheon, ⁵Department of Internal Medicine, Ewha Womans University Mokdong Hospital, Ewha Womans University School of Medicine, Seoul, ⁶Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam, ⁷Department of Clinical Epidemiology and Biostatistics, Asan Medical Center, University of Ulsan College of Medicine, Seoul, ⁸Department of Pulmonary and Critical Care Medicine, Asthma Center, and Clinical Research Center for Chronic Obstructive Airway Diseases, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea