1. Deparment of Otology, Yeplus Ear, Nose, and Throat Clinics, Ansan, Korea.
2. Department of Otolaryngology-Head and Neck Surgery, Korea University College of Medicine, Seoul, Korea.
3. Department of Otolaryngology-Head and Neck Surgery, School of Communication Sciences and Disorders, University of Iowa, Iowa City, IA, USA.
4. Department of Medical Statistics, Korea University College of Medicine, Seoul, Korea.