Quality Adjusted Life Years (QALYs) are a means of measuring both the duration and quality of life, and are typically used to measure the health benefits of medical interventions or the detriment caused by negative health effects.
A year of life lived at perfect health (or 'quality of life') is considered equal to one QALY, while a year lived in imperfect 'quality of life' would be considered to be less than a QALY. According to the National Institute for Health and Care Excellence (NICE): “Quality of life is often measured [on a 0 to 1 scale] in terms of the person's ability to carry out the activities of daily life, and freedom from pain and mental disturbance.”
- If a health condition causes a person to live one year fewer than they would have otherwise, and that year would have been lived at perfect health, that health condition has caused the loss of one QALY.
- If a health condition reduces a person's quality of life from 1 to 0.5 for two years of their life, then that health condition would have also caused the loss of one QALY.