Disability-Adjusted Life Years are a statistical measure underpinned by the principle that the life of a person with a disability is worth less the life of a person without a disability. Here we examine the ethical arguments on both sides of this metric, widely used by epidemiologists, and look to whether there may be more appropriate options available.
Important to Know:
DALYs - Disability-Adjusted Life Years - a metric developed to quantify the burden of a disease, incorporating both the number of years of life lost to death, as well as the years of life lost to disability. Within this metric, 0 represents one year spent in perfect health and 1 represents one year lost to death.
Development of DALYs
Disability-adjusted life-years (DALYs) were developed by the World Bank in the 1990s and backed by the World Health Organization (WHO) as a method of quantifying the global burden of a particular disease. [1] Whereas the more commonly-known Quality-Adjusted Life Years (QALYs) measure the gain of years of life in perfect health, DALYs measure the years of life lost in perfect health.
The weight of how living with each disability relates to its worth in terms of DALYs was determined by a panel of international experts. [2] Calculating the burden of a disease in this way allows health professionals to estimate the potential benefit that providing a certain treatment may have on improving both the duration and quality of a person’s life. In other words, DALYs aim to combine morbidity and mortality into one measure, estimating both the years of life lost to premature death and the years of life lost through disability. [2]
DALY = YLL + YLD
Disability-Adjusted Life Years = Years of Life Lost + Years Lost due to Disability
One DALY equates to one year of life lost in perfect health. Therefore, living with a "moderate disability" for ten years could be considered equal to losing five years of life in perfect health, or "five DALYs" in other words. [2]
The values in Table 1 provide some examples of the disability weights applied to a variety of diseases and conditions, arranged from least severe at the top to most severe at the bottom. A selection of conditions have been chosen to demonstrate the variation of disability weights used for the Global Burden of Disease Study in 2010.
Table 1: Disability weights used for the Global Burden of Disease Study in 2010 [3]
As a widely-used measure in epidemiology, it is important to assess both the benefits and drawbacks of DALYs, in order to determine whether there are fundamental issues which may render their use questionable.
Benefits of DALYs
As a calculator of both morbidity and mortality, DALYs are a useful tool for health professionals to determine whether an intervention will add good quality to a patient's life, as opposed to prolonging life but sacrificing good life quality. Moreover, DALYs have the added benefit of being able to measure the burden of different diseases separately, or to individually measure the DALYs lost due to separate causes contributing to one disease. This is useful for epidemiologists when assessing the absolute level of detriment caused to a population by a certain disease, which may indicate important targets for public health intervention.
Furthermore, DALYs allow the burden of physical and mental health conditions to be compared side by side. This is a useful tool for epidemiologists to compare the burden of physical and mental health problems, whilst proving beneficial in affirming mental health conditions as illnesses of equal validity to physical health conditions.
Potential Issues with DALYs
Conversely, there are several assumptions underpinning the concept of DALYs, which bring the ethics of this method into question. Firstly, the metric works on the explicit assumption that the lives of people with disabilities hold less value than those of people without disabilities. [1] This questionable assumption appears to contradict the WHO’s core ethical principle to 'respect the […] worth, equality, diversity […] of all persons'. [4] Through devaluing the lives of people with disability, this metric could be viewed as diminishing the worth and equality of these people compared to their disability-free counterparts.
Secondly, the DALY measure assumes that people living with disabilities are less entitled to receiving scarce health resources that would extend their lives than people without disabilities. [1] If a certain treatment extended life without improving quality, the DALY method would conclude that there would be a greater overall benefit in giving this treatment to perfectly healthy people than to people with a disability, because their lives, adjusted for disabilities, are worth more per year. Whilst it is unlikely that such a crude distinction would be employed in practice, especially given that no real human has ever fallen into the category of ‘perfectly healthy’, it may be worth considering whether a more complex system might be timely. It may be helpful to distinguish between individuals who are living with a disability but would not consider their quality of life to be diminished as a result, or may even feel that the value of their life has increased since living with a disability, compared to those who feel that the value of their life has decreased as a result. On the other hand, some statisticians may argue that this would reduce the reliability of the metric, through introducing subjective measures of disability severity. There is also the more intricate issue that some of the items classified as disabilities in the Global Burden of Disease, e.g. autism, are now often considered to be part of normal human variation, neurodiversity, by disability activists. [5] As such, it may be inconsistent to apply a disability weighting to a variation of normal human diversity.
What are the alternatives?
Amidst a plethora of disability rights movements campaigning for a recognition of certain disabilities to be viewed as part of a spectrum of normal human variation as opposed to holding a negative or abnormal status, it is perhaps questionable for statisticians to continue using a metric laden with potentially inappropriate labels and problematic foundations. Despite the obvious issues, it is reasonable to ask whether better options currently exist. Although there are ethical issues underpinning the principles of DALYs, they do address some key issues in epidemiology, namely how to estimate the overall damage that one disability has had on the quality and quantity of life across a whole population. It is worth examining whether an alternative method could be employed as the standard, or if there is a more helpful way of re-phrasing the concept of DALYs in line with a disability-positive narrative.
Future considerations
When learning about, or applying scientific methods, it is easy to accept the metrics currently in use without criticism. However, this example is a reminder that it is important to question the current framework and determine whether there are more appropriate methods available instead. Whether the concept of DALYs needs to be revised as an ongoing protocol, or indeed replaced altogether, there appear to be inherent issues with the current method that ought not be ignored. Whilst employing a new metric may cause obstacles when comparing the results of future studies with previous results using DALYs, this is not a sufficient reason to rule out change without considering alternative solutions.
Author: Deborah Allen, MSc in Global Health Science and Epidemiology, St Anne’s College
References:
1. T. Arnesen and E. Nord. The value of DALY life: problems with ethics and validity of disability adjusted life years. BMJ, 1999, 319 (7222), p.1423-5.
2. P. Webb and C. Bain. Essential Epidemiology : An Introduction for Students and Health Professionals, 2nd edition. Cambridge: Cambridge University Press, 2010, p.64.
3. J. A. Salomon et al. Common values in assessing health outcomes from disease and injury: disability weights measurement study for the Global Burden of Disease Study 2010. The Lancet, 2012, 380 (9859), p.2129-2143.
4. World Health Organization. Ethical Principles, [no date]. [Online] Available from: https://www.who.int/about/ethics/ethical-principles [Accessed: 28 Oct 2020].
5. N. Walker. Autistic UK: The Neurodiversity Paradigm, [no date]. [Online] Available from: https://autisticuk.org/neurodiversity/ [Accessed: 28 Oct 2020].