Background: Assessing health-related quality of life (HRQoL) among persons with dementia poses several challenges due to cognitive decline and limited perception. As a result, proxy ratings by family members or health professionals are used. The EQ-5D is the most commonly used generic and preference-based HRQoL instrument. Methodological drawbacks of the three-level version (EQ-5D-3L) prompted the development of the five-level version (EQ-5D-5L) by expanding the range in the domains. However, no comparison of the psychometric properties of both versions and different proxy ratings exist so far. Therefore, the objective of this study was to compare the psychometric properties of the EQ-5D-5L and EQ-5D-3L by application of different proxy ratings in dementia.
Methods: The EQ-5D-3L and -5L were completed by n=52 family caregivers and one care-manager at baseline and three and six months later. In total, 106 caregiver and 133 care manager proxy ratings were completed. The EQ-5D-3L and 5L were evaluated in terms of acceptability, agreement, ceiling effects, redistribution properties and inconsistency, informativity (Shannon, H', and Shannon Evenness, J', indices) as well as convergent and discriminative validity.
Results: Mean proxy index scores were higher for the 5L than the 3L. Missing values occurred less frequently in both proxy ratings and versions (<1%). Agreement between both measures was high but higher in caregiver than care-manager ratings (ICC 0.885 vs. 0.840). The relative ceiling effect decreased for the 3L compared to 5L by 56% in the caregiver- and 75% in the care-manager-rating. Inconsistency between both versions was low. Informativity increased from the 3L to the 5L version in both proxy ratings. The 5L also demonstrated a better discriminative ability than the 3L, especially in the caregiver rating. Compared with the 3L, the 5L had better convergent validity, especially for caregiver ratings.
Conclusion: The EQ-5D-5L had high feasibility and acceptability and was superior by a reduction of ceiling effects and an improvement in informativity, discriminative ability and convergent validity. Proxy ratings by informal caregivers demonstrated better psychometric properties than professional care-manager ratings.