Psychometric properties of the EQ-5D-5L in patients with hip or knee osteoarthritis: reliability, validity and responsiveness.

ABSTRACT

PURPOSE: To study the psychometric properties, including reliability, validity and responsiveness, of the Spanish EQ-5D-5L questionnaire for patients with hip or knee osteoarthritis (OA). METHODS: We included 758 patients with hip or knee OA who completed the EQ-5D-5L and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) at baseline, of whom 644 also did 6 months later. The EQ-5D-5L contains five questions from which a utility index is derived. The WOMAC covers three dimensions pain, stiffness and physical function. Floor and ceiling effects were calculated. Reliability was assessed using Cronbach's alpha. Convergent validity was tested using the Spearman correlation coefficient between EQ-5D-5L and WOMAC. We examined known-groups validity by comparing the EQ-5D-5L between subgroups defined by WOMAC scores using ANOVA or the Kruskal-Wallis test. Effect sizes were calculated to assess responsiveness, and minimal clinically important difference (MCID) was estimated. RESULTS: The EQ-5D-5L showed minimal floor and ceiling effects (< 3%). Cronbach's alpha was 0.86. The EQ-5D-5L index was strongly correlated with WOMAC pain and function scores (- 0.688 and - 0.782). Patients with higher WOMAC scores had significantly (p < 0.0001) lower EQ-5D-5L index. The 20.19% had hip or knee replacement during the follow-up. Effect sizes were small among non-surgical patients, but > 0.80 among "improved" surgical patients, being the MCID for improvement 0.32 points. CONCLUSIONS: The results support the reliability, validity and responsiveness of the EQ-5D-5L, overcoming the limitations of the EQ-5D-3L in these patients. Therefore, the EQ-5D-5L could be very useful as an outcome measure, at least in patients with hip or knee OA.