Exploration of a cultural-adaptation of the EQ-5D for Thai population: A “bolt-on” experiment
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.
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.
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 r2 0.329 vs. 0.306) but not IR (adjusted r2 0.307 vs. 0.306) significantly increased ability to predict VAS scores.
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.
KeywordsEQ-5D Health-related quality of life Bolt-on Psychometric properties Culture
This publication is a part of the degree of Doctor of Philosophy in Social, Economic and Administrative Pharmacy, Faculty of Graduate Studies, Mahidol University. This project was also funded through the Royal Golden Jubilee (RGJ) Ph.D. Programme in Thailand (Grant No. PHD/0115/2556) provided by the Thailand Research Fund (TRF) and Mahidol University. The results and opinions in this report have not been endorsed by the above funding agency. We would like to express our gratitude to the EuroQoL group for allowing us to conduct this study. We are grateful to Dr. A. Simon Pickard for his invaluable advice and comments regarding the data analyses of this study. We are thankful to the National Statistical Office (NSO) in Thailand for their help with the sampling method. Special thanks also to all local village leaders and participants from the provinces of Chumporn, Chachoengsao, Bangkok, Chaing-Mai, and Loei in Thailand who facilitated or participated in the data collection process.
Compliance with ethical standards
Conflict of interest
All authors declare that they have no conflict of interests in this study.
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