Comparative performance of EQ-5D-5L bolt-ons in China and the Netherlands: results from the EQ-DAPHNIE project

PURPOSE: This study compares the psychometric properties of eight EQ-5D-5L bolt-ons in the general populations from two culturally distinct countries: China (CN) and the Netherlands (NL). METHODS: As part of the EQ-DAPHNIE project, cross-sectional online surveys were conducted in 2024 with quota-based samples approximating the adult population from CN and the NL. Participants completed EQ-5D-5L, eight bolt-ons (vision, hearing, breathing, sleep, tiredness, social relationships, self-confidence, and cognition/memory), and sociodemographic and health-related questions. Psychometric assessments included ceiling, convergent/divergent validity, structural validity, known-groups validity, and explanatory power. RESULTS: The ceiling of the EQ-5D-5L was higher in CN (45%) than NL (32%). In both countries, vision, tiredness, and sleep bolt-ons reduced the ceiling the most, while breathing had the least effect. Tiredness and self-confidence bolt-ons demonstrated stronger associations with the core dimensions. Several bolt-ons significantly improved known-groups validity. In CN, hearing showed stronger known-groups discrimination across age groups, while self-confidence had the greatest impact in NL. The core dimensions explained more variance in EQ VAS in NL (37%) than CN (25%). In both countries, tiredness and self-confidence contributed most to increasing the variance explained. Principal component analysis (PCA) confirmed a seven-factor structure, with all bolt-ons loading separately from the core dimensions. In country-specific PCAs, no major differences were observed between CN and NL. CONCLUSION: While certain bolt-ons demonstrated robust psychometric properties in both countries, others showed greater context dependence. These findings add to the growing body of evidence supporting the development of the experimental EQ-5D Bolt-on Toolbox.