[1] Univ Ulsan, Coll Med, Dept Pulm & Crit Care Med, Asan Med Ctr, 88,Olymp Ro 43 Gil, Seoul, South Korea
[2] Univ Ulsan, Coll Med, Asan Med Ctr, Clin Res Ctr Chron Obstruct Airway Dis, 88,Olymp Ro 43 Gil, Seoul, South Korea
[3] Univ Ulsan, Dept Prevent Med, Coll Med, 88,Olymp Ro 43 Gil, Seoul, South Korea
[4] Univ Ulsan, Coll Med, Dept Clin Epidemiol & Biostat, Asan Med Ctr, 88,Olymp Ro 43 Gil, Seoul, South Korea