DALYs are one piece of information that policymakers & entrepreneurs, for instance, can use to make better decisions about how to prioritize and tackle currently intractable health challenges.

A DALY is a metric designed for the World Bank in the early 1990s to measure the burden of health conditions with greater precision – and with greater attention to the different kinds of suffering people experience – than Mortality Metrics.

While a Morality measure only counts the number (relative or absolute) of people who die from a specified set of health conditions in a specified place and time, a DALY measure looks at the “Number of years of life lost” due to disability and premature death.

DALY = YLL + YLD

A Sidebar to DALY

For example, if someone spends several years with decreased quality of life after contracting a chronic disease like heart disease at the age of 52, and then dies at the age of 60 from it, this person will be counted as 1 death in a mortality measure.

A DALY measure is more complex; Here we look at the period of time that the person lived with a decreased quality of life, and multiplied that time by a weighted approximation of how much the quality of that person’s life was reduced by the disability. Then we look at how many years the person died prematurely compared to his/her life expectancy (Let’s say in this case, 70 years of age) and add that number to the number of disability-adjusted years we calculated. This is the number of DALYs that the person lost.

This metric may then be deployed over entire populations to calculate the number of total life years lost due to disability & premature death.

In addition to helping show the additional effect of health conditions that cause disability before death, or which cause very early death as opposed to death at an old age, a DALY measure will also include certain health conditions that do not appear at all in mortality measures because they typically do not directly cause death, such as major depressive disorder or lower-back pain.

A DALY measure captures some of the suffering caused by these conditions that a Mortality measure simply cannot measure.

Source: Prof. Tarun Khanna (HarvardX)

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