Exploration of a cultural-adaptation of the EQ-5D for Thai population: A "bolt-on" experiment.

PURPOSE

As the EQ-5D was developed in western countries with only five dimensions, it might be insensitive to non-western populations including Thai. This study examined the impact of adding two candidate dimensions, "interpersonal relationships (IR)" and "activities related to bending knees (AK)," to the EQ-5D questionnaire, and evaluated their psychometric properties in a Thai population sample.

METHODS

Face-to-face interviews were conducted with 600 Thai. Ceiling effect for the EQ-5D and the EQ-5D-5L+AK+IR were compared. Spearman's rho correlation was used to determine whether the two new dimensions were redundant with the existing EQ-5D dimensions. Correlations between the two dimensions and similar dimensions of the SF-36v2 were also assessed. Hierarchical multiple regression was performed to evaluate the incremental value of the EQ-5D-5L+AK+IR over the EQ-5D in predicting VAS scores.

RESULTS

The two new dimensions were not redundant with the existing five dimensions of the EQ-5D. The highest correlation (0.371) was found between MO and AK. The overall ceiling effect decreased by 5% (50.5-45.5%) when using the EQ-5D-5L+AK+IR. Moderate correlations were found between the candidate dimensions and similar dimensions of the SF-36v2. Multiple regression indicated that adding AK (adjusted r 0.329 vs. 0.306) but not IR (adjusted r 0.307 vs. 0.306) significantly increased ability to predict VAS scores.

CONCLUSIONS

Our preliminary results suggested that AK holds promise for making the EQ-5D more relevant to Thai while it is premature to conclude on the impact of IR. Nevertheless, more work is required to carefully assess the value of the new dimensions as well as the trade-off for the modification.