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

ABSTRACTBackground: 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 r2: 0.182 vs 0.156), but not IR (adjust...