Objectives To compare EuroQol (EQ-5D) and Short form 6D (SF-6D) utility scores among multiethnic Asian patients with psoriatic arthritis (PsA).
Methods Consecutive patients fulfilling the Classification Criteria for Psoriatic Arthritis (CASPAR) for PsA and attending a tertiary rheumatology outpatient clinic were invited to complete identical English or Chinese questionnaires of EQ-5D and SF-6D and assessing socio-demographic characteristics. Utility scores were calculated using the scoring algorithms developed from the UK general population. Comparisons between the 2 instruments were performed by their score distributions, means, medians, intraclass correlation coefficients (ICCs) and Bland-Altman plot.
Results Subjects (n=86, 69 English and 16 Chinese speaking, male to female ratio 0.91) participated. Mean age (±SD) and duration of illness (±SD) were 49.1 (±13.4) and 7.1 (±8.2) years. The score distribution for SF-6D was normal while that of EQ-5D was bimodal. Ceiling and floor effects were observed in 2.3% and 20% for EQ-5D and none for SF-6D. Moderate correlations are demonstrated between the 2 scores on scale level (range 0.44-0.59) and domain level (range 0.33-0.53). The mean (±SD) EQ-5D and SF-6D utility scores were 0.74 (±0.24), [range -0.16-1.00] and 0.68 (±0.13), [range 0.36-1.00]; (p=0.001). Every 10-point increase in EQ-5D health state VAS was associated with a 0.07 and 0.04 quality-adjusted life year (QALY) gain if using EQ-5D and SF-6D respectively. EQ-5D generated higher utility scores than SF6D in subgroup with better health, and the opposite occurred in less healthy subgroup. Poor agreements between EQ-5D and SF-6D utility scores were demonstrated with the low ICC (0.43) and the Bland-Altman plot.
Conclusions Using different preference-based health-related quality of life instruments yield different utility scores, which may have a great impact on QALY estimates. This highlights the importance of choosing the appropriate instrument for cost-effectiveness evaluation. Additional research is needed to determine if EQ-5D or SF-6D is the better instrument for PsA.
Disclosure of Interest None Declared
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