QALY:
The quality-adjusted life year or quality-adjusted life-year (QALY) is a generic measure of disease burden, including both the quality and the quantity of life lived.[1][2] It is used in economic evaluation to assess the value for money of medical interventions. One QALY equates to one year in perfect health. If an individual's health is below this maximum, QALYs are accrued at a rate of less than 1 per year. To be dead is associated with 0 QALYs, and in some circumstances it is possible to accrue negative QALYs to reflect health states deemed 'worse than dead'.
DALY/Disability-adjusted life year:
The disability-adjusted life year (DALY) is a measure of overall disease burden, expressed as the number of years lost due to ill-health, disability or early death. It was developed in the 1990s as a way of comparing the overall health and life expectancy of different countries.
The DALY is becoming increasingly common in the field of public health and health impact assessment (HIA). It "extends the concept of potential years of life lost due to premature death...to include equivalent years of 'healthy' life lost by virtue of being in states of poor health or disability."[2] In so doing, mortality and morbidity are combined into a single, common metric.
Looking at the burden of disease via DALYs can reveal surprising things about a population's health. For example, the 1990 WHO report[citation needed] indicated that 5 of the 10 leading causes of disability were psychiatric conditions. Psychiatric and neurologic conditions account for 28% of all years lived with disability, but only 1.4% of all deaths and 1.1% of years of life lost. Thus, psychiatric disorders, while traditionally not regarded as a major epidemiological problem, are shown by consideration of disability years to have a huge impact on populations.
The disability-adjusted life year is a type of health-adjusted life year (HALY) that attempts to quantify the burden of disease or disability in populations. They are similar to quality-adjusted life year (QALY) measures, but rather than attach health-related quality of life (HRQL) estimates to health states that can be linked to health risks and self-reported/diagnosed sources of ill-health, DALYs assign HRQLs to specific diseases and disabilities.
Traditionally, health liabilities were expressed using one measure, the Years of Life Lost (YLL) due to dying early. A medical condition that did not result in dying younger than expected was not counted. The Years Lived with Disability (YLD) component measures the burden of living with a disability.
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