Construct validity and responsiveness of EQ-5D-3L and EQ VAS in psoriatic arthritis: an evaluation based on the Swedish Rheumatology Quality Register

PURPOSE: To evaluate construct validity and responsiveness of the health-related quality of life (HRQoL) instrument EQ-5D-3L (index, dimensions) and EQ VAS among patients with psoriatic arthritis (PsA). METHODS: This retrospective, register-based study utilised data from the Swedish Rheumatology Quality Register. Known-groups validity was assessed by comparing EQ-5D-3L and EQ VAS results across groups with varying levels of physical function or disease activity. Convergent validity was assessed through correlations with comparator instruments. Responsiveness was assessed by analysing correlations between changes in EQ-5D-3L, EQ VAS, and comparator instruments, as well as by assessing the ability to discriminate between patients who improved and those who did not, using the area under the receiver operating characteristic curve (AUC). To confirm construct validity or responsiveness, ≥ 75% of hypotheses had to be supported. RESULTS: The study included 13,105 patients with PsA. EQ-5D-3L and EQ VAS demonstrated moderate to strong correlations with comparator instruments and found expected differences between groups with varying physical function or disease activity. Over 75% of the hypotheses related to construct validity were supported. Regarding responsiveness, several hypotheses for the EQ-5D-3L were not supported, and none of the AUC-related hypotheses for EQ VAS were supported. Overall, less than 75% of the hypotheses related to responsiveness for EQ-5D-3L and EQ VAS were supported. CONCLUSION: The results from this observational study support construct validity of EQ-5D-3L and EQ VAS among patients with PsA. However, responsiveness was not supported for the EQ-5D-3L dimensions which suggests that the EQ-5D-3L may not fully capture changes in HRQoL from interventions impacting other dimensions than pain/discomfort.