QALY

Quality-adjusted life year (QALY) is a measure used in health economics to assess the value of medical interventions. It combines quantity and quality of life into a single metric, enabling comparisons across different health technologies and programs.

Calculation and interpretation: QALYs are calculated by multiplying the number of years of life gained or lived in a given health state by a utility weight that reflects the quality of those years. A year in perfect health has a weight of 1, while a year in a health state with a weight between 0 and 1 has that value. Some models allow negative weights for states considered worse than death. Utility weights are typically derived from population surveys using instruments such as the EQ-5D, HUI, or SF-6D. Future QALYs are commonly discounted at a rate (often around 3% per year) to reflect time preference.

Applications: QALYs are central to cost-utility analysis, used to compare the value of different health interventions and to inform resource allocation in health technology assessment. Decision makers often use a threshold for cost per QALY gained to judge whether an intervention is cost-effective. Thresholds vary by country and payer; for example, some public health systems reference ranges of roughly £20,000 to £30,000 per QALY in the United Kingdom, with higher ranges sometimes considered.

Limitations and ethical considerations: QALYs rely on subjective valuations that may differ across individuals and cultures. They can be influenced by the choice of instrument and the sampling of respondents. Critics argue that QALYs may undervalue certain outcomes, such as end-of-life care or benefits to disabled populations, and raise equity concerns about distribution of health gains.

Example: If a treatment extends life by 2 years with a quality weight of 0.8, it yields 1.6 QALYs.