Mapping the English and Chinese versions of the Functional Assessment of Cancer Therapy-General to the EQ-5D utility index

Abstract

Objective: This study aims to develop a function for mapping the English and Chinese versions of the Functional Assessment of Cancer Therapy-General (FACT-G) scores to the EuroQoL Group's EQ-5D utility index and to test whether a single function is sufficient for the two language versions.

Methods: A baseline survey of 558 cancer patients in Singapore using the FACT-G and EQ-5D was conducted (308 English and 250 Chinese questionnaires). Regression models were used to predict the EQ-5D utility index values based on the FACT-G scores and thus derive a mapping equation. Data from a follow-up survey of the patients were used to validate the results.

Results: The FACT-G Social/Family scale was not associated with the EQ-5D utility index (P = 0.701). There was no interaction between language version and the predictors (each P > 0.1). An equation that maps the FACT-G Physical, Emotional, and Functional well-being scales to the EQ-5D utility index was derived. In the validation sample, the mean observed utility values was larger than the mapped by only 0.005 (95% confidence interval [CI]-0.006 to 0.016), but the mean absolute difference was 0.083 (95% CI 0.076 to 0.090).

Conclusions: At the group level, but not individual level, the equation developed can accurately map the English and Chinese versions of the FACT-G scores to the EQ-5D utility index.