*Geek Box: Disability-Adjusted Life-Years [DALYs]
While epidemiology tends to focus on ‘hard’ outcomes in terms of events, e.g., myocardial infarction or lung cancer, these events may only represent the endpoint of a long disease process. With chronic lifestyle diseases, it is common for individuals to be treated for the disease before an event occurs.
Thus, it is important to not only be able to quantify the incidence of events, but the amount of years a person lives disease-free. If people are diagnosed with a disease at a younger age, this means a greater number of the lifespan is spent combating a disease.
Disability-adjusted life years [DALYs] are a method of quantifying the burden of disability associated with a disease, and reflect the number of years spent dealing with an illness or disability, and premature death, within a population. DALYs are calculated by adding the number of years of life lost to the number of years spent living with an illness or disability. Thus, DALYs estimate the sum of both premature death and years spent with illness.
The life years lost is based off average life expectancy in the population. By using the reference standard life expectancy, it is possible to use DALYs to summarise population health, because DALYs can reflect a gap in health, i.e., the actual state of population health compared to the ideal goal [which is for people to live the full life expectancy with full health]. It is possible to quantify DALYs by age, sex, and location, to provide absolute measures of the years of healthy life lost due to illness and death and provide meaningful comparisons across different populations and groups.