To compare the EuroQol (EQ-5D) and Short Form 6D (SF-6D) among multiethnic Asian patients with knee osteoarthritis (OA) scheduled for total knee replacement in Singapore.
Patients were asked to complete questionnaires including the EQ-5D, Short Form 36, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Lequesne knee index. EQ-5D and SF-6D utility scores were calculated using the scoring algorithms developed from the UK general population. Agreement between the 2 instruments was assessed by comparing their score distributions, means, medians, intraclass correlation coefficients (ICCs), and a Bland-Altman plot. Correlations of the EQ-5D and SF-6D with WOMAC and Lequesne knee index scores were also examined.
A consecutive sample of 258 knee OA patients (127 English-speaking and 131 Chinese-speaking) participated. The mean +/- SD EQ-5D utility score was 0.49 +/- 0.31 (range -0.25-1.00) and the mean SF-6D utility score was 0.63 +/- 0.12 (range 0.32-0.89). In a hypothetical example, this 0.14-point difference in mean utility scores yielded a difference of $10,000/quality-adjusted life year (QALY) in cost-effectiveness ratios. The score distribution was bimodal for the EQ-5D and normal for the SF-6D. This poor agreement was also demonstrated by the Bland-Altman plot and the low ICC (range 0.18-0.54). Correlations of the WOMAC and Lequesne index with the EQ-5D were higher than with the SF-6D.
Using different preference-based health-related quality of life instruments may yield different utility scores, which could have a great impact on QALY estimates. This highlights the importance of selecting appropriate instruments for economic evaluation. Additional research is needed to determine which instrument (the EQ-5D or the SF-6D) should be used in OA patients.