DALY and QALY

Disability-adjusted life years or DALYs are a measurement of disease burden, which is the impact of a health problem on an individual or in a population.

Typically, disability-adjusted life years are used to compare the burden of two diseases, like type II diabetes - which is a chronic condition where the body doesn’t produce enough insulin - and malaria - which is an infectious disease spread by mosquitoes that causes a person to have flu-like symptoms.

These two diseases are usually hard to compare because they affect different populations, have different short-term and long-term complications, and are managed completely differently.

So, to compare the two diseases, you could calculate the disability-adjusted life years for both diabetes and malaria, and the disease with the highest disability-adjusted life years has the highest disease burden.

Disability-adjusted life years are particularly useful for helping determine how resources should be allocated to a specific health issue.

For example, if you have 100 thousand dollars to donate, do you want to spend it towards helping people with type II diabetes in Canada or helping people with malaria in India?

So let’s try to calculate the disability-adjusted life years for diabetes in Canada, and that requires knowing two things.

First, you need to know the years of life lost to premature death, or YLL.

The years of life lost is calculated by multiplying the number of deaths that were the result of the disease (N), and the standard life expectancy at the age of death (L).

The standard life expectancy is just the average life expectancy in a population minus the age of the person who died.

For example, the average life expectancy in Canada is 82 years old, so the standard life expectancy of a person at age 60 is 22 years, because 82 minus 60 is 22. And if we’re only talking about 1 person who died, the number of deaths is 1.

So the years of life lost for a 60-year-old person that died from diabetes would be 1 times 22, or 22 years.

Calculating the years of life lost for an entire population gets a little more complicated, since a population is usually made up of people in different age groups.

For example, let’s say you want to figure out the burden of diabetes in a population of 4,000 people randomly selected in Canada.

So, you recruit 1,000 individuals in each of the 4 different age categories - 0 to 19, 20 to 49, 50 to 79, and above 80 - and follow them for 10 years.

You find out that there was 1 death from diabetes in the youngest age group, then 3, 4, and 7 deaths in the older age groups.