Development of a Functioning Measurement Scale for the South Korean Population Using the Korea National Health and Nutrition Examination Survey

Objectives This study aimed to develop a functioning metric for the Korean general population using the Korea National Health and Nutrition Examination Survey (KNHANES) and to evaluate its psychometric properties. Methods A Partial Credit Model (PCM) calibrated functioning items from KNHANES on a 0–100 scale. Psychometric properties examined, including item fit, unidimensionality, local item dependency (LID), targeting, and differential item functioning (DIF) across age, sex, and region. Results Using data from 5,413 adults, 14 functioning items were used to construct the metric. Model fit was achieved through a testlet solution. Item fit and unidimensionality were acceptable, with no LID observed. Reliability was adequate, though targeting indicated items were easy for the sample. Limited DIF by age was detected. Conclusion This study developed a standardized, policy-relevant functioning metric using national health data. The developed functioning metric captures lived health and complements traditional indicators of mortality and morbidity. The study highlights the value of repurposing routine survey data for monitoring population health. Given increasing demand for health assessment in ageing societies, this metric supports evidence-based policymaking and long-term planning for Korea.