Konstantina Skaltsa1, Louise Longworth2, Cristina Ivanescu3, De Phung4, Stefan Holmstrom4. 1. Quintiles, Barcelona, Spain; Faculty of Medicine, University of Barcelona, Barcelona, Spain. Electronic address: konstantina.skaltsa@quintiles.com. 2. Health Economics Research Group, Brunel University, Uxbridge, UK. 3. Quintiles, Hoofddorp, The Netherlands. 4. Astellas Pharma Global Development, Leiden, The Netherlands.
Abstract
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.
RCT Entities:
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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