Development of a Short Form of the Life Functioning Scale for Older Adults in the Korea National Health and Nutrition Examination Survey

Abstract Purpose Lengthy national health surveys impose a substantial respondent burden on older adults. This study aimed to develop and validate a short form of the 25-item Life Functioning (LF-25) scale to reduce this burden. Methods Two candidate short forms were generated by combining item response theory (IRT)-based item selection with qualitative content validation. Following baseline administration to 519 adults aged 50 years and older, a 10-item scale (LF-10) was selected. The psychometric properties of the LF-10 were subsequently tested in an independent sample of 263 older adults. Predictive validity was evaluated by regressing six-month health outcomes on baseline LF-10 scores in a follow-up subsample. Results A graded response model showed acceptable fit (RMSEA = 0.07), and confirmatory factor analysis supported a unidimensional structure. The LF-10 correlated strongly with both the original LF-25 and a criterion Physical Functioning scale. Internal consistency was excellent (McDonald's ω = 0.93), and test–retest reliability was excellent (intraclass correlation coefficient = 0.94). Baseline LF-10 scores significantly predicted physical functioning and self-rated health at the six-month follow-up. Conclusions The LF-10 is a valid, reliable, and efficient measure of physical functioning in older adults that halves administration time relative to the LF-25. It has been adopted by the Korean Frailty and Aging Cohort Study (2023) and the Korea National Health and Nutrition Examination Survey (2024), supporting its feasibility for national health surveillance.