1. Division of Pulmonology; Department of Internal Medicine; Severance Hospital; Institute of Chest Diseases; Yonsei University College of Medicine; Seoul Korea
2. Biostatistics Collaboration Unit; Yonsei University College of Medicine; Seoul Korea
3. 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
4. Department of Radiology and Research Institute of Radiology; Asan Medical Center; University of Ulsan College of Medicine; Seoul Korea