Mapping the English and Chinese versions of the Functional Assessment of Cancer Therapy-General to the EQ-5D utility index.
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.
Cheung
Yin-Bun
YB
Clinical Trials and Epidemiology Research Unit, Singapore. yinbun@cteru.com.sg
Thumboo
Julian
J
Gao
Fei
F
Ng
Gim-Yew
GY
Pang
Grace
G
Koo
Wen-Hsin
WH
Sethi
Vijay-Kumar
VK
Wee
Joseph
J
Goh
Cynthia
C
D000223:Adaptation, Psychological; D000465:Algorithms; D003625:Data Collection; D005260:Female; D006305:Health Status Indicators; D006801:Humans; D007802:Language; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D009369:Neoplasms / Q000523:psychology* / Q000628:therapy; D011594:Psychometrics; D011788:Quality of Life / Q000523:psychology*; D012044:Regression Analysis; D012846:Singapore; D011795:Surveys and Questionnaires / Q000592:standards*