Quality-Adjusted Life Years (QALYs)
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1. Core Knowledge:
A population health indicator that combines the quantity and quality of life. It is typically used to indicate the output of a new therapy on a whole-population basis.
The QALY extends the idea of life expectancy by incorporating an indicator of the quality of life among survivors. This helps to address the question of whether extending life expectancy (e.g., by life-saving therapies) may also increase the number of sick and disabled people in society. So, rather than count every year of life lived in a population as though they were equivalent, this statistic adjusts years lived in a state of disability or incapacity downwards: they are counted as being worth less than a full year of healthy life.
QALYs are calculated as the average number of additional years of life gained from an intervention, multiplied by a utility judgment of the quality of life in each of those years. For example, a person might be placed on hypertension therapy for 30 years, which prolongs his life by 10 years at a slightly reduced quality level of 0.9. In addition, the need for continued drug therapy reduces his quality of life by 0.03. Hence, the QALYs gained would be 10 x 0.09 - 30 x 0.03 = 8.1 years. The valuations of quality may be collected from surveys; a subjective weight is given to indicate the quality or utility of a year of life with that disability.
The idea of QALYs can also be applied to years of life lost due to sickness, injuries or disability. This can illustrate the societal impact of disease. For example, a year lived following a disabling stroke may be judged worth 0.8 normal years. Imagine a person aged 55 years who lives for 10 years after a stroke and dies at age 65. In the absence of the stroke he might be expected to live to 72 years of age, so he has lost 7 potential years. As his last 10 years were in poor health, they were quality-adjusted downward to an equivalent of 8 years, so the quality-adjusted years of life lost would be 7 + (10 - 8), or 9.
Updated September 4, 2014
Quality versus quantity of life...