Outcomes from treatments and other health-influencing activities have two basic components - the quantity and quality of life.
The QALY has been created to combine the quantity and quality of life.
It takes one year of perfect health-life expectancy to be worth 1, but regards one year of less than perfect life expectancy as less than 1.
Thus an intervention which results in a patient living for an additional four years rather than dying within one year, but where quality of life fell from 1 to 0.6 on the continuum will generate:
- 4 years extra life @ 0.6 quality of life values 2.4
- less 1 year @ reduced quality (1 - 0.6) 0.4, and
- QALYs generated by the intervention 2.0
QALYs can therefore provide an indication of the benefits gained from a variety of medical procedures in terms of quality and life and survival for the patient.
A measure that combines mortality and quality of life gains (outcome of a treatment measured as the number of years of life saved, adjusted for quality).
QALYs are calculated by estimating the total life-years lost due to a disease or gained by a treatment and weighing each year with a quality-of-life score (from o, representing worst health, to 1 or 100, representing best health) to reflect the quality of life in that year.
World Health Organization. European Observatory on Health Systems and Policies. Glossary. 2009.