Disability Adjusted Life Years (DALY)

According to the World Health Organization, the Disability Adjusted Life Year (DALY) can be thought of as one lost year of "healthy" life. The sum of these DALYs across the population, or the burden of disease, can be thought of as a measurement of the gap between current health status and an ideal health situation where the entire population lives to an advanced age, free of disease and disability. The measurement takes into account both actual life lost and the equivalent loss through disability.

The disability weight is used to determine the number of equivalent years of good health which are lost per year of disability. A person who has lost a leg would be deemed to have a 30 percent disability weight. Therefore, for every 10 years of additional life lived, he would be considered to have lost three years.

But years of life lived with disability are not necessarily "lost" years, nor can they always correctly be described as years "burdened" by disease. According to the World Health Organization, disability is not an illness. Equating disability with illness has led to confusion as is evident in the DALYs, where researchers attempt to classify disability states based upon the International Statistical Classification of Diseases.

Indeed, most individuals experiencing disability are not continually in need of medical care, nor are they continually too ill to function. Becoming disabled can occur at any point in the life span and the majority of individuals with a disability will live for years with little or no medical assistance. For most, the bulk of their life-span will be lived outside the province of the medical sector. Their lot in life will be considerably more comfortable and productive if they have access to resources and technical aids, such as hearing aids, eye glasses, or wheelchairs; or environmental or architectural changes such as ramps, grab bars and large print newspapers that will allow them more independence and self-sufficiency. But these individuals will not simply disappear should these resources not be forthcoming.

Another fundamental concern is that the DALYs are, by their very nature, subjective. A growing body of research has found that able-bodied people are more likely to assign a poorer quality of life to living with a disability than do those who actually live with a disability.

Studies have also found that able-bodied medical professionals who deal with disability, the very experts who were asked to assess the quality of life with disablement, are particularly likely to see the whole of an individuals' life in terms of medical needs rather than seeing health care or rehabilitation to be one component of a fuller life.

The social and economic implications of living with a disability constitute an equally significant point left unanswered by the Disability-Adjusted Life Years scale. The past two decades have brought a growing realization that the quality and achievement associated with an individual's life depend in large measure on the socio-cultural, legal and economic ramifications of living with a disability. The U.N. World Program of Action clearly states that the quality of life with disability reflects the interrelationship between an individual and his or her environment. The WHO's International Classification of Impairments, Disabilities and Handicaps (ICIDH) has endeavored to more accurately define disability by emphasizing the social context within which individuals must live. The DALYs are unable to address disability in a context wider than that of the individual. For example, using the ICIDH model, a spinal cord injury resulting in paraplegia may prove far more "handicapping", both socially and economically, to a sugar cane cutter than to a college professor. The identical loss of sight for an impoverished washerwoman living in a shanty town and a wealthy urban woman might produce very different ramifications; indeed the second woman's need for assistance in home or career may create jobs for one or more individuals. According to the DALYs, both men with paraplegia and both women with severe vision loss would be equally burdensome to their societies, but in the real world the issues that affect their lives are economic and social, not medical.

The social subjectivity of the procedure for valuing disability in the Disability-Adjusted Life Years scale becomes even more complex when viewed from a cross-cultural perspective. Whereas the standardization of measurement of the disability itself has been shown to be possible cross-culturally, it has been shown that the value attached to any disability state varies markedly between cultures.

For example, how can one use the DALY to quantify the value of disability for an individual with a slight disability, such as walking with a limp, in a society where such a disability would make it difficult to marry and unmarried adults are not allowed to fully participate in the community? (Whyte and Ingstad: 1995) How significant is profound deafness if enough hearing individuals use sign language to allow easy communication? (Groce: 1985).

Moreover, ideas about the causes and consequences of disability are often embedded in specific cultural belief systems. In countries with a number of distinct cultural groups, the weighing system of the quality of life with disability for DALYs would need to be adjusted for each distinct ethnic or tribal group.

This tribal prejudice is specifically addressed in the McIlvaine Tribal Factor concept discussed below. The disagreement over the weight of any disability can also be resolved through the use of the life Quality Offset concept.

Quality Adjusted Life Years (QALY)

QALY is defined as perfect health minus DALY. The basic idea underlying the QALY is simple:  It assumes that a year of life lived in perfect health is worth 1 QALY (1 Year of Life 1 Utility = 1 QALY) and that a year of life lived in a state of less than this perfect health is worth less than one. In order to determine the exact QALY value, it is sufficient to multiply the utility value associated with a given state of health by the years lived in that state. QALYs are therefore expressed in terms of "years lived in perfect health":  Half a year lived in perfect health is equivalent to 0.5 QALYs (0.5 years 1 Utility), the same as one year of life lived in a situation with utility 0.5 (e.g. bedridden) (1 year 0.5 Utility).

In the last two decades, QALYs have become increasingly widely used as a measure of health outcomes. This is largely due to three important characteristics. First, the QALY combines changes in morbidity (quality) and mortality (amount) in a single indicator. Second, QALYs are easy to calculate via simple multiplication, although the prior estimation of utilities associated with particular health states is a more complicated task. Finally, QALYs form an integral part of one particular type of economic analysis within healthcare, i.e. cost-utility analysis.

To submit comments, please e-mail me at: rmcilvaine@mcilvainecompany.com