DALY: What Is It, How to Calculate It, and Why Is It Important
The Disability Adjusted Life Year, or DALY, is a health metric that quantifies the number of years lost due to premature death or disability. In other words, it captures the overall burden of disease in a population.
Public health researchers and practitioners use DALYs as a way to compare different conditions and risk factors since they provide a common language for understanding the relative impact of different health problems. In this article, we’ll take a deep dive into DALY, what it is, how it’s calculated, and why it matters.
What is Disability Adjusted Life Year (DALY)?
Disability Adjusted Life Years (DALY) is a measure of life years lost due to disease or early death, adjusted for assumptions about disability as well as the impact of age and future time. It is an attempt to assess the global burden of disease by region of the world and to bring together results from various cost-effectiveness analyses of health interventions by disease using one outcome measure.
One DALY can be thought of as one lost year of a healthy life. The sum of these DALYs across the population is a measurement of the gap between the current health status and an ideal health situation where everyone lives to an advanced age, free of disease and disability.
How to calculate Disability Adjusted Life Years (DALYs)?
Here’s how you can calculate DALYs:
- Calculate the Years of Life Lost (YLL) by multiplying the number of deaths by the remaining life expectancy at the age of death.
- Calculate the Years Lived with Disability (YLD) by multiplying the number of prevalent cases with a certain health outcome by the disability weight assigned to this health outcome.
- Sum up the YLLs and YLDs. Namely, DALY = YLL + YLD.
- DALY is measured on a scale between 0 and 1, with 0 implying perfect health and 1 equals death.
Why Is It Important To Calculate DALYs?
1. DALYs provide a summary measure of the burden of disease in a population
The calculation of DALYs provides a summary measure of the burden of disease in a population by considering the impact of both mortality and morbidity and combining them into a single number. This metric enables experts, health policymakers, and researchers to assess the burden of diseases on a population and take a large-scale view of how these conditions can affect the ability of individuals to live healthy lives.
2. DALYs provide a measure of population health that can be used to compare populations over time.
DALYs can be used to compare populations over time by looking at the difference between the current health status of a population and an ideal situation in which everyone lives to the standard life expectancy and is in perfect health.
For example, DALY scores can be used to compare the impact of certain conditions, such as growing cases of diabetes, heart disease, or physical disabilities, on the ability to live a long, healthy life in different parts of the world.
3. DALYs can be used to identify high-priority health interventions.
DALYs can be used to identify high-priority health interventions. For example, if a particular country has a high burden of a specific disease, like cardiovascular disease, that would be an excellent candidate to prioritize intervention.
4. DALYs can be used to estimate the cost-effectiveness of health intervention
DALYs can be used to estimate the cost-effectiveness of health interventions by comparing the cost of the intervention to the number of DALYs it has averted. This calculation can be done by determining a DALY’s monetary value. This is typically done by calculating the cost per Quality-Adjusted Life Year (QALY) and then converting that to a cost per DALY.
For example, let’s say a health intervention costs $100 and is estimated to avert 10 DALYs. To determine the cost-effectiveness of this intervention, we need to know the monetary value of a DALY. Let’s assume that a QALY is worth $5000. To convert that to a cost per DALY, we divide 5000 by 1.67 (which is the number of DALYs in a QALY). This gives us a value of $2994.01 for a DALY.
We then divide the cost of the intervention ($100) by the value of a DALY ($2994.01), which gives us a cost-effectiveness of $0.03 per DALY averted. This means that for every $0.03 spent on the intervention, 1 DALY is averted. This data can be of extremely high value in the Health Economics and Outcomes Research (HEOR) area.
5. DALYs are useful for assessing progress toward health-related Sustainable Development Goals
DALYs (Disability-adjusted Life-Years) can be used to assess progress toward health-related Sustainable Development Goals (SDGs). This metric combines the burden of mortality and morbidity (non-fatal health problems) into a single number, making it an effective tool for measuring the impact of different diseases on a population.
6. DALYs can be used to assess equity in health between different groups in a population
DALYs can be used to assess equity in health between different groups in a population by comparing the total disease burden between the groups. The total burden of disease is calculated by adding up the DALYs associated with each condition (mortality plus morbidity). This can reveal disparities in health outcomes across different population groups. For example, if there is a significant disparity in the DALYs associated with a particular condition, it could be an indication of inequitable access to healthcare or other resources.
7. DALYs can be used to assess the burden of key neglected diseases
DALYs can be used to assess the burden of key neglected diseases by calculating the amount of healthy life lost due to mortality and morbidity caused by the disease. This is done by taking into account the disability weights assigned to different diseases, as found in Lopez et al. (2006), which measure the impact of the disease on quality of life.
DALYs are a metric used to measure the impact of disability on life expectancy. They provide an overview of the burden of disease on a population and can be used to track the impact of health interventions and measure progress toward global health targets. The data collected can then be used by HEOR experts and improve healthcare around the globe.