Quality-adjusted life years (QALYs) are currently considered the most appropriate generic measure of health benefit, according to the manual of the National Institute for Health and Care Excellence (NICE) in the United Kingdom. QALYs can be compared across diseases areas and healthcare systems.
In a single number, QALYs capture the extent to which a treatment prolongs or increases the quantity of life (reduced mortality) and the quality of life (reduced morbidity). QALYs measure multiple dimensions of health outcomes: each health state is described using the five dimensions of mobility, self-care, ability to carry out usual activities, pain/discomfort, and anxiety/depression. Figure 1 illustrates how three alternative treatments may affect the quantity and quality of life. Treatment A offers a shorter quantity and lower quality of life than treatment C. Treatment B offers shorter quantity but higher quality of life than treatments A and C.
How quality of life is calculated depends on the context: the NICE manual, for example, recommends weighting health states according to the preferences of the target population. Thus, for a population that prefers longer life to healthier life, QALYs would be higher for treatments A and C than for B. The converse would be true for a population that prefers healthier to longer life.
Figure 1. Quality and quantity of life of treatments A, B, C
In health economics, a given intervention is associated with a certain number of quality-adjusted life years, a measure that adjusts the quantity of life after that intervention (survival years) by the quality of life after the intervention (weight).
QALYs are computed in several steps:
- Description of the dimensions of outcomes of interest (i.e., what should count?),
- Estimation of health states from clinical evidence,
- 3. Valuation of each health state using generic preference-based measures of health,
- Discounting of the individual utility scores,
- Multiplication of the duration of time spent in each health state by the weight estimated in step 2 and aggregation of these utility scores within a time horizon. QALYs range between 0 and 1 for states equivalent to death and full health, respectively.
In the United Kingdom, NICE considers QALYs as the most appropriate measure of mortality and morbidity. In the United States, the Institute for Clinical and Economic Review recommends the use of QALYs as well as other measures of health outcomes, such as Equal Value of Life Years Gained (evLYG).