2.1. Study Design and Setting

The KNHANES is a nationwide, population-based, cross-sectional survey designed to assess the health and nutritional status of the Korean population and to evaluate health policies and programs in Korea. The survey is conducted annually in 192 regions of Korea, with a sample size of approximately 10,000 people each year. The data are from the 7th Korea National Health and Nutrition Examination Survey (KNHANES). The KNHANES is conducted by the Korea Disease Control and Prevention Agency. As our study is based on data from the Patient Health Questionnaire (PHQ-9), which is administered every two years, we examined two years of data from the 2016 and 2018 surveys. Trained medical staff, dieticians, health interviewers, and medical technicians conducted every stage of the study either at a mobile screening center or in participants’ homes. Written informed consent from participants was approved by KNHANES. The study was conducted according to the guidelines of the Declaration of Helsinki and approved by the Institutional Review Board of Gyeongsang National University Changwon Hospital (protocol code: GNUCH 2021-09-007 and date of approval: 23 September 2021).