Validity and interpretation of preference-based measures of health-relatedquality of life

Utilities are numeric measurements that reflect an individual's beliefs abo ut the desirableness of a health condition, willingness to take risks to ga in health benefits, and preferences for time. This report discusses the app roaches to assess and compare the validity of methods used to assign utilit ies for cost-utility analysis. Threats to validity include construct underr epresentation and construct-irrelevant variance. Construct underrepresentat ion occurs when a stimulus presented to a judge fails to fully represent th e depth and complexity of information required in actual judgments. Constru ct-irrelevant variation occurs when factors irrelevant to preferences influ ence measurements of utilities. Among several factors that cause construct- irrelevant variation are cognitive abilities, numeracy skills, emotions and prejudices, and the elicitation procedure. Commonly used elicitation metho ds (visual-analog scales, time tradeoff, and standard gamble) capture diffe rent facets of utilities (desirableness of states, time preferences, and ri sk attitude) to different degrees. The validity of an elicitation protocol depends (1) on the degree to which its scaling method captures the relevant facets of utility and (2) on the degree to which measurements are influenc ed by construct-irrelevant variation. Discrete-state health index models pr ovide an alternative to direct elicitation of utilities and work by attachi ng fixed preference weights to observable health states. The creation of di screte-state models with current technologies requires the adoption of stro ng assumptions about the scaling properties of utilities. Future research m ust refine methods of eliciting utilities and identify sources of construct -irrelevant variability that reduce the validity of utility assessments. Be cause of the impact of variation in techniques on measurements, we do not r ecommend the combination of utilities elicited with different protocols in cost-utility analysis and do not recommend the display of cost-utility rati os from different studies in comparison or "league" tables.