<human>:  What is the QALY?
<bot>: The QALY is a measure of the quality of life gained from a medical intervention. It is a measure of the change in quality of life over time. The QALY is calculated by multiplying the number of years of life gained by the quality of life gained. For example, if a medical intervention increases the quality of life by 10%, then the QALY is 10 years of life gained multiplied by 10%.