Deriving a patient-based utility index from a cancer-specific quality of life questionnaire

Objectives: The aim of this study was to derive a scoring algorithm for a validated disease-specific quality of life instrument called the Utility-Based Questionnaire-Cancer (UBQ-C) that provided a utility index designed to inform clinical decisions about cancer treatments. Methods: The UBQ-C includes a scale for global health status (1 item); and subscales for physical function (3 items), social/usual activities (4 items), self-care (1 item), and distresses because of physical and psychological symptoms (21 items). A scoring algorithm was derived to convert the subscales into a subset index, and combine it with the global scale into an overall health-related quality of life (HRQL) index, which was converted to a utility index with a power transformation. The valuation survey consisted of 204 advanced cancer patients who completed the UBQ-C and assigned time trade-off (TTO) utilities about their own health state. Preliminary validation involved comparing these derived utilities with other measures of HRQL. Results: Weights for the subset index were: physical function 0.28, social/usual activities 0.06, self-care 0.01, and distresses 0.64. Weights for the overall HRQL index were health status 0.65 and subset index 0.35. The mean of the utility index scores was similar to the mean of the TTO utilities (0.92 vs. 0.91, P = 0.6). The utility index was substantially correlated with other measures of HRQL. Conclusions: Data from a simple, self-rated, disease-specific questionnaire can be converted into a utility index suitable for comparing the net effect of cancer treatments on quality of life, and to evaluate trade-offs between quality and quantity of life in quality-adjusted survival analyses.