The DALY Approach: So it’s imperfect. Can you do better?

So the DALY (Disability-adjusted life year) approach is not perfect. Here’s a reminder to its critics: neither is the majority of data that is used in global health policy. Rather, global health policy is a numbers game and often times the numbers used are the result of generalization and guestimation.

For example, the International Classification of Disease (ICD) was an attempt by the WHO to create an international standard for disease classification. However, different manifestations of certain diseases and the varying knowledge of and adherence to the ICD classification system within and among countries, results in the data regarding cause of death to be flawed.

Similarly, data regarding the lives of the poor in developing countries is imperfect. Whereas in the United States, vital registration systems are in place for recording births and deaths, most developing countries lack such systems. While we also rely on facility surveys to get population health information, this too is insufficient because it can only generate data for people who actually come to the facility. This means poor people who cannot afford to travel to facilities or pay for their services, as well as indigenous peoples who prefer traditional medicine to western medicine and therefore do not use health facilities are not included in facility surveys. This is problematic because poor and indigenous people constitute large portions of the population in many countries and not having health data on them could drastically alter public health policy decisions.

Although public health professionals are continuously searching for feasible, more reliable data gathering techniques, the fact is that global health policies tend to be formulated in environments with little and low-quality data. This is important to note because critics of the WHO’s DALY system, which is used to estimate the global burden of disease, seem to be comparing it to a perfect, 100% accurate measurement and the fact is that such a measurement does not exist. Therefore while certain criticisms of DALY are legitimate and should be considered, we must also recognize that most data used in public health is flawed and remember that slightly imperfect data is better than no data at all.

There are several standard arguments that critics of DALY make. The first is that the forced consistency of the two disability weighting questions (the first compares the value of extended life in people without disabilities with that in disabled people; the second asks subjects to value cures for different chronic conditions relative to interventions that extend life) makes the disability weights arbitrary. Critics claim that forcing subjects to choose answers that result in the same disability weighting changes their original answer and makes the disability weight lose meaning. Critics then argue that the validity of the global burden of disease report is decreased.

My response to this argument is, “Would it better be better to disregard the report completely when forming public health policy?”  I think not. As long as policymakers are cognizant of the fact that the global burden of disease report is not the Holy Grail, but rather a single tool that can be used to influence the policymaking process, the report has the chance of helping make sure policy decisions address the strongest public health threats.

Similarly, critics argue that the DALY approach is unethical, as the method assumes that the lives of disabled people are less valuable than the lives of able-bodied people and time discounting favors middle-aged people over the elderly and infants. When it comes to determining how to allocate society’s money, I see nothing wrong with considering the benefit that individual will be able to contribute to society if fully healed. Murray explains “unequal age weights as an attempt to capture different social roles at different ages…higher weights for a year of time at a particular age does not mean that the time lived at that age is per se more important to the individual, but that because of social roles the social value of that time may be greater” (Sudhir Anand and Kara Hanson, “Disability-adjusted life years: a critical review”, 691). The reality is that not everyone can be healed. So, why not heal the members of society that have the greatest likelihood of contributing to society once they are healed?

Along the same lines, critics fail to acknowledge that the DALY approach is an improvement over past approaches to measuring the burden of disease. For example, the DALY approach is more comprehensive than the Potential Years of Life Lost (PYLL) model, which considers only causes of mortality and does not take into consideration time lived with disabilities. This improvement led to some unexpected findings. For example, the DALY approach revealed that Neuropsychiatric disorders and injuries were the major causes of years of healthy life lost due to disability (YLD), a fact that was vastly underappreciated when measuring mortality alone (Alan Lopez, et al, “Global Burden of Disease and Rick Factors”, 2). Hence, while still not perfect, the DALY approach improved on prior models and has increased understanding regarding the global burden of disease.

In conclusion, I would like to reiterate that while there are certainly ways in which the DALY approach could be improved, it should not be forgotten that this approach revolutionized how the global burden of disease is determined and is still the strongest tool we have for determining the global burden of disease.


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