What is a quality-adjusted life year (QALY)?
How QALYs combine length and quality of life, and what they tell us about the value of healthcare.
Updated
A quality-adjusted life year combines time lived with a value for health-related quality of life. One year in full health equals one QALY.
A simple example
Imagine a person lives for two years with a health-state utility of 0.8 throughout. They accrue 2 × 0.8 = 1.6 QALYs. This is an illustrative calculation, not a prediction for a specific patient.
When quality of life changes over time, calculate the QALYs for each period and add them together. A treatment can generate additional QALYs by extending life, improving quality of life, or both.
What does a utility value mean?
Utility values are usually anchored at 1 for full health and 0 for death. Some value sets assign negative values to health states valued as worse than death. Utilities are preference-based measures; a patient's questionnaire score is not automatically a utility value.
Instruments such as EQ-5D describe health states. A relevant value set converts those descriptions into utilities. The instrument, value set and population should fit the evaluation.
Using QALYs to compare care
An economic evaluation compares the difference in expected QALYs between an innovation and its comparator. That difference, together with additional costs, informs the incremental cost-effectiveness ratio.
QALYs support comparisons but do not describe every aspect of value. Affordability, equity, patient preferences and practical implementation also matter.