Factor structure and measurement invariance of the EuroQol 5-dimensional questionnaire: a secondary analysis of the Korea Health Panel survey

Objectives: This study evaluated the EuroQol 5-dimensional questionnaire, 3-level version (EQ-5D-3L), using Korea Health Panel (KHP) data by examining its factor structure, measurement invariance across gender and age groups, and longitudinal measurement invariance. Methods: Panel 1 data from the second survey year (2009), when the EQ-5D-3L was first introduced in the KHP, through the 12th year (2017) were analyzed, along with panel 2 data from 2019 to 2021. Confirmatory factor analysis and measurement invariance tests by gender and age groups were conducted within each period. Longitudinal measurement invariance was also evaluated for each period. Results: A 1-factor model demonstrated good fit for the EQ-5D-3L. In panel 1, full measurement invariance across gender and age groups was supported. In panel 2, partial invariance was achieved after relaxing constraints on item 5. Longitudinal measurement invariance was supported over 5- and 10-year intervals in panel 1 and over a 3-year interval in panel 2, indicating temporal stability of the measurement model. Conclusion: The EQ-5D-3L used in the KHP panel 1 and panel 2 datasets demonstrates a stable 1-factor structure and acceptable measurement invariance across key subgroups and over time. These findings support the use of the EQ-5D-3L as an appropriate instrument for assessing health-related quality of life among Korean adults and for longitudinal analyses within large-scale panel surveys.