Comparison of EuroQol-5D and short form-6D utility scores in multiethnic Asian patients with psoriatic arthritis: a cross-sectional study.

OBJECTIVE: To compare EuroQol-5D (EQ-5D) and Short Form-6D (SF-6D) utility scores in multiethnic Asian patients with psoriatic arthritis (PsA).

METHODS: Consecutive patients fulfilling the Classification Criteria for Psoriatic Arthritis attending a rheumatology outpatient clinic were recruited and completed the EQ-5D and SF-6D questionnaires. Comparisons were performed by score distribution, mean, median, and the Outcome Measures in Rheumatology filter: i.e., truth, discrimination, and feasibility.

RESULTS: Eighty-six patients were enrolled (69 English-speaking and 17 Chinese-speaking; male:female ratio 0.91). The score distribution of SF-6D was normal, while that of EQ-5D was bimodal. A ceiling effect was observed in 20% of patients for EQ-5D and none for SF-6D. There were moderate correlations (Spearman's rho = 0.59, p < 0.0001) between the 2 scores, but poor agreements on scatterplot, intraclass correlation (ICC 0.43 and standardized ICC 0.21), and Bland-Altman plots. EQ-5D generated lower utility scores than SF-6D in the poorer health subgroup. SF-6D had stronger correlation with the general health status and other external measures of health; and it distinguished better between good and poor general health status, with better effect size and relative efficiency statistics. EQ-5D demonstrated higher patient acceptability.

CONCLUSION: EQ-5D and SF-6D instruments generated different utility scores in PsA. SF-6D may be superior because of normal scaling distribution and the absence of ceiling and floor effects. SF-6D also had better construct validity and better discrimination of poor health status. More studies are required for cost-utility analysis in PsA.