A comparison of EQ-5D index scores using the UK, US, and Japan preference weights in a Thai sample with type 2 diabetes

BACKGROUND Data are scarce on the comparison of EQ-5D index scores using the UK, US, and Japan preference weights in other populations. This study was aimed to examine the differences and agreements between these three weights, psychometric properties including test-retest reliability, convergent and known-groups validity, and the impact of differences in the EQ-5D scores on the outcome of cost-utility analysis in Thai people. METHODS A convenience sample of 303 type 2 diabetic outpatients (18 years or older) from a cross-sectional study was examined. ANOVA and pos-hoc Bonferroni tests were used to determine the differences among the three EQ-5D scores. The agreements among the EQ-5D scores were assessed employing intraclass correlations coefficients (ICCs) and Bland-Altman plots. The ICCs were utilized to examine the test-retest reliability. Spearman's rho correlation coefficients were used to assess the convergent validity between the EQ-5D scores and sociodemographic & clinical data, and health status. Mann-Whitney U tests were used to test the differences in EQ-5D scores between the known groups including HbA1c level (cut point of 7%), and the presence of diabetic complications namely neuropathy, retinopathy, nephropathy and cardiovascular diseases. Seven hypothetical decision trees were created to evaluate the impact of differences in the EQ-5D scores on the incremental cost-utility ratio (ICUR). RESULTS The US weights yielded higher scores than those of the UK and the Japan weights (p < 0.001, both), while the UK and the Japan weighted scores did not differ (p > 0.05). Both UK and US scores had more agreement with each other than with the Japan scores. Regarding psychometric properties, the Japan scheme provided better test-retest reliability, convergent and known-groups validity than both UK and US schemes. The variation in EQ-5D scores estimated from UK, US, and Japan preference weights had a marginal impact on ICUR (range: 1.23-6.32%). CONCLUSION Since the Japan model showed more preferable psychometric properties than the UK and the US models and the differences in these EQ-5D scores had a small impact on ICUR, we recommended that for both clinical and policy purposes the Japan scheme should be used in Thai people. However, more research needs to be done.