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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." 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 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. == Calculation == 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. DALYs are calculated by taking the sum of these two components: : The DALY relies on an acceptance that the most appropriate measure of the effects of chronic illness is time, both time lost due to premature death and time spent disabled by disease. One DALY, therefore, is equal to one year of healthy life lost. How much a medical condition affects a person is called the ''disability weight'' (DW). This is determined by disease or disability and does not vary with age. Tables have been created of thousands of diseases and disabilities, ranging from Alzheimer's disease to loss of finger, with the disability weight meant to indicate the level of disability that result from the specific condition. At the population level, the burden of disease as measured by DALYs is calculated by DALY = YLL + YLD where YLL is years of life lost, and YLD is years lived with disability. In turn, population YLD is determined by the number of years disabled weighed by level of disability caused by a disability or disease using the formula YLD = I x DW x L. In this formula I = number of incident cases in the population, DW = disability weight of specific condition, and L = average duration of the case until remission or death (years). There is also a prevalence (as opposed to incidence) based calculation for YLD. Premature death is calculate by YLL = N x L, where N = number of deaths due to condition, L = standard life expectancy at age of death (expectancy - age at death).〔(【引用サイトリンク】url=http://www.who.int/healthinfo/global_burden_disease/metrics_daly/en/ )〕 Japanese life expectancy statistics are used as the standard for measuring premature death, as the Japanese have the longest life expectancies. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Disability-adjusted life year」の詳細全文を読む スポンサード リンク
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