A quality-adjusted life-year, abbreviated as QALY, is a mathematically derived measurement intended to capture both quality and quantity of life. It’s used in many cost effectiveness studies, and its purpose is to assess the benefit from a particular intervention or outcome, even if that outcome is simply survival. QALY It takes into account a person’s life expectancy (quantity) as well as the quality of those remaining years.
Deeper dive
Researchers may calculate how many QALYs are gained by a particular treatment, intervention or preventive measure, or they may calculate how many are lost by not using a particular intervention or due to some event that happens, such as the loss of QALYs following a stroke or a specific cancer diagnosis.
The actual formula for calculating QALYs is multiplying the number of remaining years by a number intended to represent the utility value of each of those years: 1 represents a year of perfect health/quality, and 0 represents death. For example, if taking a particular medication for a chronic condition extends that person’s life by 10 years, but each of those years will have a slightly reduced quality estimated at 0.8, then the QALY increase from taking that medication is 8 QALYs (10 x 0.8). (That example is oversimplified because the need to take medication would be factored in as reducing quality of life as well.)