title: Mapping the FACT-G cancer-specific quality of life instrument to the EQ-5D and SF-6D.
abstract: OBJECTIVE
  To help facilitate economic evaluations of oncology treatments, we mapped responses on cancer-specific instrument to generic preference-based measures.
  
  
  METHODS
  Cancer patients (n = 367) completed one cancer-specific instrument, the FACT-G, and two preference-based measures, the EQ-5D and SF-6D. Responses were randomly divided to form development (n = 184) and cross-validation (n = 183) samples. Relationships between the instruments were estimated using ordinary least squares (OLS), generalized linear models (GLM), and censored least absolute deviations (CLAD) regression approaches. The performance of each model was assessed in terms of how well the responses to the cancer-specific instrument predicted EQ-5D and SF-6D utilities using mean absolute error (MAE) and root mean squared error (RMSE).
  
  
  RESULTS
  Physical, functional, and emotional well-being domain scores of the FACT-G best explained the EQ-5D and SF-6D. In terms of accuracy of prediction as measured in RMSE, the CLAD model performed best for the EQ-5D (RMSE = 0.095) whereas the GLM model performed best for the SF-6D (RMSE = 0.061). The GLM predicted SF-6D scores matched the observed values more closely than the CLAD and OLS.
  
  
  CONCLUSIONS
  Our results demonstrate that the estimation of both EQ-5D and SF-6D utility indices using the FACT-G responses can be achieved. The CLAD model for the EQ-5D and the GLM model for the SF-6D are recommended. Thus, it is possible to estimate quality-adjusted life years for economic evaluation from studies where only cancer-specific instrument have been administered.
authors.affiliation: Canadian Centre for Applied Research in Cancer Control, British Columbia Cancer Agency, Vancouver, BC, Canada. pteckle@bccrc.ca.
authors.forename: Paulos
authors.initials: P
authors.lastname: Teckle
authors.forename: Helen
authors.initials: H
authors.lastname: McTaggart-Cowan
authors.forename: Kim
authors.initials: K
authors.lastname: Van der Hoek
authors.forename: Stephen
authors.initials: S
authors.lastname: Chia
authors.forename: Barb
authors.initials: B
authors.lastname: Melosky
authors.forename: Karen
authors.initials: K
authors.lastname: Gelmon
authors.forename: Stuart
authors.initials: S
authors.lastname: Peacock
mesh_terms: D000328:Adult; D000368:Aged; D001943:Breast Neoplasms / Q000523:psychology*; D001955:British Columbia; D015179:Colorectal Neoplasms / Q000523:psychology*; D005260:Female; D006801:Humans; D016014:Linear Models; D008175:Lung Neoplasms / Q000523:psychology*; D008297:Male; D057240:Patient Preference; D011788:Quality of Life / Q000523:psychology*; D019057:Quality-Adjusted Life Years; D011795:Surveys and Questionnaires / Q000592:standards*