Mapping the FACT-P to the preference-based EQ-5D questionnaire in metastatic castration-resistant prostate cancer.
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.
['Skaltsa|Konstantina|K|', 'Longworth|Louise|L|', 'Ivanescu|Cristina|C|', 'Phung|De|D|', 'Holmstrom|Stefan|S|']
D000368:Aged D000465:Algorithms D004311:Double-Blind Method D006801:Humans D016015:Logistic Models D008297:Male D008875:Middle Aged D015233:Models, Statistical D009362:Neoplasm Metastasis D011237:Predictive Value of Tests D064129:Prostatic Neoplasms, Castration-Resistant D011788:Quality of Life D011795:Surveys and Questionnaires
mapping FACT-P EQ-5D metastatic castration-resistant prostate cancer quality of life