Measuring Patients Preferences and Utilities

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In addition to measuring descriptive quality of life, it is possible to measure a patient's preference, or utility, for particular health states. This can be accomplished by assessing a patient's value for one health state compared with another based on quality-of-life considerations. For example, two patients might report similar symptoms with similar frequency and duration, but they may differ on how important these symptoms are in their daily lives. Descriptive quality-of-life instruments will correctly provide similar scores for these two patients, whereas a measurement of preference or utility will differentiate them.

Utility is measured on a scale from 0 to 1, where 0 denotes a health state ''as bad as death'' and 1 denotes a health state ''as good as perfect health.'' Values between 0 and 1 denote degrees between these extremes. A simple interpretation of a utility for a specific health state, A, is that the utility represents the amount of time in a state of perfect health that a patient values as equal to one unit of time in state A. For example, suppose that state A has a utility of 0.7. Then 1 month in state A is equivalent in value to 0.7 months of perfect health. This interpretation leads to the idea that quality-of-life-adjusted time can be obtained by multiplying a health state duration by its utility coefficient. For example, if a patient experiences 6 months of toxicity and has a utility weight of 0.8 for time with toxicity, then the quality-adjusted time spent with toxicity is 4.2 months. This adjustment allows treatments that have different impacts on quality of life to be compared in a meaningful way.

Classically, utility assessment is carried out using interview techniques. The ''standard gamble'' technique gives patients a choice between a chronic health state with certainty or an uncertain health state that is either perfect health (with probability p) or death (with probability 1 - p). The probability p is varied until the patient is indifferent between the certain and the uncertain choice and the final p is taken as the utility value. The ''time trade-off'' technique gives patients a choice between living for a certain amount of time in a state of less than perfect health or a shorter amount of time in a state of perfect health. The duration of the ''perfect health'' state is varied until the patient expresses indifference to the choice. The utility is then taken as the ratio of the final health state durations. For a detailed overview of utility assessment, see Bennett and Torrance (13).

Interview techniques are cumbersome to use in practice. Fortunately, there are procedures for obtaining utility data from quality-of-life instruments using multiattribute utility theory (14). Generally, these procedures were developed by administering both the instrument and the interview to a study sample and building a statistical model for predicting the utility value from the instrument responses. Instruments that can be used for this purpose include the EuroQol (15),

Health Utilities Index (16), and the Q-tility Index (17), which uses Spitzer's Quality of Life Index (18).

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The Complete Compendium Of Everything Related To Health And Wellness

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