The KNHANES is a collection of nationally representative, cross-sectional, population-based health, and nutritional surveys produced by the Korean Centers for Disease Control and Prevention. Briefly, participants in KNHANES were chosen by proportional allocation sampling with multistage stratification, based on geography, age, and sex. KNHANES includes a health interview, physical examination, laboratory tests, and nutritional questionnaires to assess the health and nutritional status of the noninstitutionalized civilian population of Korea. The health interview included an established questionnaire to determine the demographic and socioeconomic characteristics of the subjects including age, education level, occupation, income, marital status, smoking habits, alcohol consumption, exercise, past and current diseases, and family history. A field survey team including otorhinolaryngologists performed the interviews and physical examinations in a mobile examination unit. All individuals participated voluntarily and provided their written informed consent. The KNAHENS protocol was approved by the Korean Centers for Disease Control and Prevention institutional review board.