2.1. Data

Study data were obtained from the Korea National Health and Nutrition Examination Survey (KNHANES), which was conducted by the Korea Center for Disease Control and Prevention Agency. The KNHANES is a nationwide survey that is annually conducted to evaluate health behavior and health status since 1998. The data set selected for this study was between 2016 and 2019. The health survey and demographic data were collected via medical screening vehicle with necessary medical equipments for physical measurement part, and the nutrition survey was conducted by visiting the target household in person. Medical screening vehicle is a traveling checkup center, usually in a form of a bus, and exist for sociodemographically or economically underprivileged people who have high barrier access to medical utilization. However, in this case, it was used for anthropometric data collection of the targeted study population. Items related to education and economic activities, morbidity, medical use, and nutrition survey items were asked in‐person by fieldworkers. The health behavior items of the survey, such as smoking and drinking, were self‐reported. A representative sample were extracted for the target population, who are 1 year and older and residing in Korea. As for the sampling method, two‐step stratified colony sampling method is applied with the survey district and household as the first and second extraction units. Response rates in 2016, 2017, 2018 and 2019 of KNHANES were 75.4%, 77.9%, 76.5%, and 74.7% each. A total of 32 379 individuals participated in the survey for four consecutive years. Due to the feature of cross‐sectional study, overlapping individuals by year were not removed, but they were regarded as another individual study participant. The data from these surveys are used to monitor and estimate the prevalence of chronic diseases and citizens' health in the South Korean population. ^{16 , 17}