Reliability, validity and responsiveness of two multiattribute utility measures in patients with chronic obstructive pulmonary disease.

The objective of the study was to evaluate the reliability, validity and responsiveness of two generic multiattribute methods for measuring utility for health states: a 15-dimensional (15D) and a five-dimensional method (EuroQol and EQ-TTO). A self-administered questionnaire with both measures was used in 59 outpatients with chronic obstructive pulmonary disease and the findings compared with standard gamble (SG) and time trade-off (TTO) utilities, spirometry and arterial blood gases. Quality of life scores were smallest for EQ-TTO (median 0.73) and highest for SG and TTO (median 0.91 and 0.95 respectively), while 15D gave intermediate values (median 0.80). The test-retest reliability over 14 days was: 15D (p = 0.90) and EQ-TTO (p = 0.73), using Spearman's rank correlation. 15D was better than EQ-TTO at discriminating between groups of patients after reported global rating of change over 12 months (P = 0.004 versus P = 0.09), indicating that 15D was more responsive. The 15D instrument has many attractive properties when compared to the EQ-TTO method, including a better reliability and responsiveness. Validity depends on validation method. The findings in this study indicate that the different utility measures measure different aspects of health-related quality of life (HRQoL). Caution should be taken when choosing utility instruments in cost-utility studies, as this can strongly influence the results.