1. Department of Otolaryngology, Faculty of Medicine, Chiang Mai University, Chiang Mai 50000, Thailand
2. Department of Otorhinolaryngology, Faculty of Medicine, Siriraj Hospital, Mahidol University, Bangkok 10700, Thailand
3. Division of Clinical Epidemiology, Department of Community Medicine, Faculty of Medicine, Chiang Mai University, Chiang Mai 50000, Thailand
4. Clinical Research Center, Faculty of Medicine, Thammasat University, Pathum Thani 12120, Thailand