Disability-adjusted life years
Encyclopedia
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. Originally developed by Harvard University for the World Bank in 1990, the World Health Organization
subsequently adopted the method in 2000. 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.
Traditionally, health liabilities were expressed using one measure: (expected or average number of) Years of Life Lost (YLL)
. This measure does not take the impact of disability into account, which can be expressed by: Years Lived with Disability (YLD).
DALYs are calculated by taking the sum of these two components. In a formula:
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. Japan
ese life expectancy statistics are used as the standard for measuring premature death, as the Japanese have the longest life expectancies.
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.
and receiving a return on its investment in educating children. Society has invested relatively little in very young children, and it has already received a substantial return on its investment in older people. Young adults, however, have received the maximum amount of investment and, at the beginning of their working life, have had the least opportunity for society to benefit from its investment.
The global burden of disease
(GBD) 2001-2002 study counted life years equally, but the GBD 1990 and GBD 2004 studies used the following formula:
W = 0.1658 Y e-0.04 Y
Where Y is the age at which the year is lived and W is the value assigned to it relative to an average value of 1.
In these studies future years were also discounted at a 3% rate, so that a weighted year of life saved next year is worth 97% of a year of life saved this year.
The effects of the interplay between life expectancy and years lost, discounting, and social weighting are complex, depending on the severity and duration of illness. For example, the parameters used in the GBD 1990 study generally give greater weight to deaths at any year prior to age 39 than afterward, with the death of a newborn weighted at 33 DALYs and the death of someone aged 5–20 weighted at approximately 36 DALYs.
(25.1/1,000), cardiovascular (23.8/1,000), mental problems (17.6/1,000), neurological (15.7/1,000), chronic respiratory (9.4/1,000) and diabetes (7.2/1,000) are the main causes of good years of expected life lost to disease or premature death.
and the World Bank
known as the global burden of disease study
, which was published in 1990. It is now a key metric employed by the United Nations
World Health Organization
in such publications as its Global Burden of Disease
Disease burden
Disease burden is the impact of a health problem in an area measured by financial cost, mortality, morbidity, or other indicators. It is often quantified in terms of quality-adjusted life years or disability-adjusted life years , which combine the burden due to both death and morbidity into one...
, expressed as the number of years lost due to ill-health, disability or early death. Originally developed by Harvard University for the World Bank in 1990, the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
subsequently adopted the method in 2000. The DALY is becoming increasingly common in the field of public health
Public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...
and health impact assessment
Health Impact Assessment
Health Impact Assessment is defined as "a combination of procedures, methods and tools bywhich a policy, program or project may be judged as to its potential effects on the...
(HIA). It "extends the concept of potential years of life lost due to premature death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
...to include equivalent years of ‘healthy’ life lost by virtue of being in states of poor health or disability
Disability
A disability may be physical, cognitive, mental, sensory, emotional, developmental or some combination of these.Many people would rather be referred to as a person with a disability instead of handicapped...
." In so doing, mortality
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
and morbidity are combined into a single, common metric.
Traditionally, health liabilities were expressed using one measure: (expected or average number of) Years of Life Lost (YLL)
Years of potential life lost
Years of potential life lost or potential years of life lost , is an estimate of the average years a person would have lived if he or she had not died prematurely. It is, therefore, a measure of premature mortality. As a method, it is an alternative to death rates that gives more weight to deaths...
. This measure does not take the impact of disability into account, which can be expressed by: Years Lived with Disability (YLD).
DALYs are calculated by taking the sum of these two components. In a formula:
- DALY = YLL + YLD.
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. Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
ese life expectancy statistics are used as the standard for measuring premature death, as the Japanese have the longest life expectancies.
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
Mental illness
A mental disorder or mental illness is a psychological or behavioral pattern generally associated with subjective distress or disability that occurs in an individual, and which is not a part of normal development or culture. Such a disorder may consist of a combination of affective, behavioural,...
. Psychiatric
Psychiatry
Psychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...
and neurologic
Neurology
Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...
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
Epidemiology
Epidemiology is the study of health-event, health-characteristic, or health-determinant patterns in a population. It is the cornerstone method of public health research, and helps inform policy decisions and evidence-based medicine by identifying risk factors for disease and targets for preventive...
problem, are shown by consideration of disability years to have a huge impact on populations.
Social weighting
A crucial distinction among DALY studies is the use of "social weighting", in which the value of each year of life depends on age. Commonly, years lived as a young adult are valued more highly than years spent as a young child or older adult. This weighting system reflects society's interest in productivityProductivity
Productivity is a measure of the efficiency of production. Productivity is a ratio of what is produced to what is required to produce it. Usually this ratio is in the form of an average, expressing the total output divided by the total input...
and receiving a return on its investment in educating children. Society has invested relatively little in very young children, and it has already received a substantial return on its investment in older people. Young adults, however, have received the maximum amount of investment and, at the beginning of their working life, have had the least opportunity for society to benefit from its investment.
The global burden of disease
Global burden of disease
The global burden of disease is a comprehensive regional and global assessment of mortality and disability from 107 diseases and injuries and ten risk factors. The GBD is assessed using the GBD study by the World Health Organization , and is an example of an evidence-based input to public health...
(GBD) 2001-2002 study counted life years equally, but the GBD 1990 and GBD 2004 studies used the following formula:
W = 0.1658 Y e-0.04 Y
Where Y is the age at which the year is lived and W is the value assigned to it relative to an average value of 1.
In these studies future years were also discounted at a 3% rate, so that a weighted year of life saved next year is worth 97% of a year of life saved this year.
The effects of the interplay between life expectancy and years lost, discounting, and social weighting are complex, depending on the severity and duration of illness. For example, the parameters used in the GBD 1990 study generally give greater weight to deaths at any year prior to age 39 than afterward, with the death of a newborn weighted at 33 DALYs and the death of someone aged 5–20 weighted at approximately 36 DALYs.
Australia
CancerCancer
Cancer , known medically as a malignant neoplasm, is a large group of different diseases, all involving unregulated cell growth. In cancer, cells divide and grow uncontrollably, forming malignant tumors, and invade nearby parts of the body. The cancer may also spread to more distant parts of the...
(25.1/1,000), cardiovascular (23.8/1,000), mental problems (17.6/1,000), neurological (15.7/1,000), chronic respiratory (9.4/1,000) and diabetes (7.2/1,000) are the main causes of good years of expected life lost to disease or premature death.
PTSD rates for the 25 most populous countries
A table comparing the PTSD DALY rates for the world's 25 most populous countries may be found in the Epidemiology section of the Wikipedia Posttraumatic stress disorder (PTSD) article. Comparison of this rate across these countries makes clear that the region of the world most impacted by PTSD is Asia.History and usage
The DALY was first conceptualized by Murray and Lopez in work carried out with the World Health OrganizationWorld Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
and the World Bank
World Bank
The World Bank is an international financial institution that provides loans to developing countries for capital programmes.The World Bank's official goal is the reduction of poverty...
known as the global burden of disease study
Global burden of disease
The global burden of disease is a comprehensive regional and global assessment of mortality and disability from 107 diseases and injuries and ten risk factors. The GBD is assessed using the GBD study by the World Health Organization , and is an example of an evidence-based input to public health...
, which was published in 1990. It is now a key metric employed by the United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...
World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...
in such publications as its Global Burden of Disease