Adding two culture-specific ‘bolt-on’ dimensions on the Thai version of EQ-5D-5L: an exploratory study in patients with diabetes

Background: This study explored whether addition of culture-specific bolt-on dimensions, ‘interpersonal relationships (IR)’ and ‘activities related to bending knees (AK)’ improves the relevance and validity of the EQ-5D among Thai patients with diabetes. Methods: A cross-sectional study was conducted among 200 diabetic patients. Ceiling/floor effects, known-groups validity and test-retest reliability were evaluated. Hierarchical multiple regressions was performed to evaluate the incremental value of the EQ-5D+AK+IR over the EQ-5D-5L in predicting utility measured by visual analog scale (VAS). Results: The EQ-5D+AK+IR reduced ceiling effects by 34%. For known-groups validity, women and lower educated patients reported more AK problems (p-value< 0.05); however, none of the IR dimension hypotheses were supported. Both IR and AK had the weighted kappa coefficients of 0.49, indicating good reliability. Hierarchical multiple regression found that adding AK (adjusted r ² : 0.182 vs 0.156), but not IR (adjusted r ² : 0.157 vs 0.156) significantly increased the explained variance in VAS score. Conclusion: Preliminary findings suggest that AK, but not IR, may be a useful addition to the EQ-5D questionnaire for use with Thai patients. Further studies in diverse populations are needed to examine the impacts of the proposed new dimensions and determine if these cultural adaptations are justified.