1. Department of Otolaryngology-Head & Neck Surgery, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan
2. Department of Epidemiology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama University, Okayama, Japan
3. Department of Otolaryngology, Kawasaki Medical School, Kurashiki, Japan
4. Department of Otolaryngology, School of Medicine, International University of Health and Welfare, Narita, Japan