Journal
VALUE IN HEALTH
Volume 17, Issue 2, Pages 238-244Publisher
ELSEVIER SCIENCE INC
DOI: 10.1016/j.jval.2013.12.005
Keywords
EQ-SD; FACT-P; mapping; metastatic castration-resistant prostate cancer; quality of life
Funding
- Medivation, Inc.
- Astellas Pharma, Inc.
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Objectives: To develop a mapping algorithm for estimating EuroQol five dimensional (EQ-5D) questionnaire values from the prostate cancer-specific health-related quality-of-life (HRQOL) instrument Functional Assessment of Cancer Therapy-Prostate (FACT-P) instrument Methods: The EQ-5D questionnaire and FACT-P instrument data were collected for a subset of patients with metastatic castration-resistant prostate cancer in a multicenter, randomized, double-blind, placebo-controlled phase 3 trial. We compared three statistical techniques to estimate patients' EQ-5D questionnaire index scores determined by using the UK tariff: 1) generalized estimating equations, 2) two-part model combining logistic regression and generalized estimating equation, and 3) separate mapping algorithms for patients with poor health defined as a FACT-P score of 76 or less (group-specific model). Four different sets of explanatory variables were compared. The models were cross-validated by using a 10-fold in-sample cross-validation. Results: Values for both instruments were available for 236 patients with metastatic castration-resistant prostate cancer. The group-specific model including the FACT-P subscale scores and baseline variables had the best predictive performance with R-2 0.718, root mean square error 0.162, and mean absolute error 0.117. The two-part model and the generalized estimating equation model including the FACT-P subdomain scores and baseline variables also had good predictive performance. Conclusions: The developed algorithms for mapping the FACT-P instrument to the EQ-5D questionnaire enable the estimation of preference-based health-related quality-of-life scores for use in cost-effectiveness analyses when directly elicited EQ-5D questionnaire data are missing.
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