Health Utility and Quality-Adjusted Life-Years

Health utility measurement assigns a value, anchored between death and full health, to states of health, so that time spent in a given state can be weighted by its quality. Combining these utility weights with length of life yields the quality-adjusted life-year (QALY), a generic measure that captures both how long and how well a person lives and lets the health gains of very different interventions be compared on a single scale.

Definition

A health utility is a preference-based value for a health state, conventionally scaled so that full health equals one and death equals zero; the quality-adjusted life-year combines these utility weights with time, so that one year in full health equals one QALY and time in worse health counts for proportionally less.

Scope

This topic covers the concept of a health-state utility, the methods used to elicit it, the construction of the QALY, the multi-attribute instruments commonly used to generate utility values, and the main criticisms of the approach. It is a methodological reference and does not value any individual's health state or recommend care.

Key concepts

• Health-state utility (0 = death, 1 = full health)
• Quality-adjusted life-year (QALY)
• Time trade-off and standard gamble elicitation
• Visual analogue scale
• Multi-attribute utility instruments (e.g. EQ-5D, Health Utilities Index)
• Value sets and population preferences
• QALY weighting and equity considerations

Mechanisms

Utility values are obtained either by directly eliciting preferences for described health states or by using a multi-attribute instrument that classifies a person's health and then maps that classification to a value through a pre-scored value set derived from population preferences. Direct methods include the standard gamble, which frames the value of a state as the risk of death a person would accept to avoid it, and the time trade-off, which frames it as the length of life a person would give up to be in full health; the visual analogue scale offers a simpler rating but is not formally preference-based. The resulting utility weight multiplies the time spent in the state to produce QALYs: ten years at a utility of 0.7 equal seven QALYs. Because the QALY combines quantity and quality of life in one generic unit, it allows cost-utility analyses across diverse conditions to share a common denominator, which is why it is central to much economic evaluation. The standardisation of how QALYs should be estimated and reported is addressed by methodological panels.

Clinical relevance

QALYs and health-state utilities are the outcome measure in most cost-utility analyses that inform health-technology appraisal, so understanding them helps clinicians and students interpret why interventions are compared as they are. The topic describes a population-level measurement framework; it does not assign value to any individual's life or health and is not a basis for clinical decisions about a patient.

Evidence & guidelines

Foundational methodology is set out by Torrance (1986) for health-state utility measurement and by Weinstein and Stason (1977) for the use of QALYs in cost-effectiveness analysis; the EQ-5D instrument was introduced by the EuroQol Group (1990); reporting and estimation conventions are addressed by the Second Panel on Cost-Effectiveness in Health and Medicine (Sanders and colleagues, 2016) and Drummond and colleagues' textbook.

History

The idea of weighting life-years by health quality emerged in health economics in the 1970s, with Weinstein and Stason among those who embedded QALYs in cost-effectiveness analysis and Torrance formalising the measurement of health-state utilities. The 1990 introduction of the EQ-5D gave the field a widely used, brief, preference-based instrument, and subsequent value sets and methodological panels standardised practice, while debate continued over the QALY's ethical and distributional assumptions.

Debates

Does the QALY embed contestable value judgements?

Treating a QALY as equal regardless of who receives it, and deriving utility weights from population rather than patient preferences, raise equity and fairness questions; critics argue the measure may disadvantage older or more severely ill people, while proponents value its transparency and comparability.

Key figures

• George Torrance
• Milton Weinstein
• the EuroQol Group
• Gillian Sanders

Seminal works

• torrance-1986
• weinstein-stason-1977
• euroqol-1990

Frequently asked questions

What is a quality-adjusted life-year?

It is a year of life weighted by the quality of health during that year, on a scale where full health is one and death is zero. One year in full health is one QALY; a year in a state valued at 0.5 counts as half a QALY.

How are health-state utility values obtained?

They are elicited through preference-based methods such as the time trade-off or standard gamble, or generated by classifying health with a multi-attribute instrument like the EQ-5D and mapping it to a value set derived from population preferences.