This JAMA Guide to Statistics and Methods reviews how health state utility assessment can be used to calculate quality-adjusted life-years, a patient-specific measure of preference for health outcomes that incorporates quantity and quality of life.
Health state utilities are used to provide quantitative measures of how strongly a person values a certain health state.1 Distinct from other patient-reported outcome measures, which may not be based on preference, utilities estimate a person’s preference for an outcome, such as sexual dysfunction, which may be very different from another person’s.2 Utilities are measured on a scale of 0 to 1, in which 0 represents a health state equivalent to death and 1 represents a health state of perfect health. In a recent study, Faris et al3 used multiple direct methods, including the visual analog scale, time trade-off, and standard gamble, to assess respondents’ preferences for 5 health states related to facial palsy and its treatment using facial reanimation surgery.
Why Is Health State Utility Assessment Used?
Although survival or freedom from some major event such as myocardial infarction are important treatment outcomes, they do not explicitly account for a patient’s quality of life. The quality-adjusted life-year (QALY) was developed to measure health outcomes in terms of both quantity and quality.1 QALYs are calculated by multiplying the duration of time spent in a health state by the utility associated with that health state; for instance, 1 year spent in perfect health (1 year × a utility value of 1) is equal to 1 QALY. Totaling the QALYs accumulated by a patient during a specified follow-up period provides a summary measure of the health outcomes achieved.
Description of Direct Methods for Utility Assessment
To measure utilities, health states of interest must first be defined. Selection of the health states typically depends on the health states and events required for the eventual economic model. Descriptions of the health states are often developed from several sources, such as patient and physician interviews, trial data, and published literature.4 People are then asked to evaluate these health states to assign them a numerical value.
Depending on the goal of the study, participants may include members of the general public, patients with a disease who have not yet experienced the health state, or patients with a disease who are experiencing the health state.5 Patients may be more familiar with their health states than members of the general public; however, the general public may be more relevant for the development of economic models used to guide allocation of societal resources.6
Direct methods for utility assessment ask respondents about their preferences for health states. The simplest method for directly assessing preferences is the visual analog scale. When using the visual analog scale, ...