Quality-Adjusted Life Years (QALYs)

What is a Quality-Adjusted Life Year?

One of the problems faced by decision makers is how to compare health interventions across diseases and with different health outcomes for priority setting in healthcare. A QALY-like concept was first proposed by Herbert Klarman in 1968 in a study of chronic kidney disease that estimated that quality of life was 25% better with transplant compared with dialysis. The method and premise was further developed in the 1970s, with the term quality-adjusted life year and QALY first being popularized by M. C. Weinstein and W. B. Stason in 1977. The underlying premise of this metric was to refer diverse health outcomes, such as lives saved, improved life expectancy, improvements in quality of life, functionality, or symptom control, back to the same value scale such that it would be possible to compare these diverse health outcomes with each other. When combined with information about the costs of alternative healthcare interventions, QALYs form the basis of cost-utility analysis; an incremental cost-utility ratio (or a cost per QALY gained) indicates the additional cost of one intervention compared with another that is required to generate 1 extra year of perfect health. QALYs are also referred to by different names; for example, the U.S. National Center for Health Statistics calls them years of healthy life (YHL), and Statistics Canada uses a variety of terms, including health-adjusted life years (HALYs) and health-adjusted life expectancy (HALE).

By capturing changes in both mortality (life expectancy) and morbidity (quality of life) related to a healthcare intervention, and combining them into a single outcome, the QALY offers advantages over health outcomes measured in natural units, for example, survival, because it is (a) likely to better capture the true scope of health-related effects of an intervention and (b) also provides a common metric by which diverse programs and interventions can theoretically be compared in terms of costs and consequences. For priority setting, the QALY metric therefore allows consideration of the [Page 933]relative efficiency of wide-ranging interventions across different disease states.

Calculation

A QALY is calculated by weighting the time spent in different health states by how desirable that health state is. These weights are variously referred to as QALY weights, QOL weights, utility weights, and HRQOL (health-related quality of life) weights. These terms are often used interchangeably in the literature, although they are not strictly equivalent. The term QALY weight is used here. To operationalize the QALY metric, weights are needed to represent the health-related quality of life of different health states. QALY weights have a number of properties:

• 1.
  They are based on preferences; more preferred health states have a higher weight than less preferred; the weights should be based on a sample of individual preferences, obtained in a way that involves a trade-off between quality and quantity of life.
• 2.
  They are bounded on perfect health and death.
• 3.
  They measure strength of preference on a cardinal (interval) scale, with equal intervals measured in such a way that they have equal value.

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