What are DALYs and are they a good metric?

What are DALYs

Disability Adjusted Life-Years (DALYs) are a measure of how many years of healthy life are lost due to early death or debilitating condition. According to the WHO, “the sum of these DALYs across the population, or the burden of disease, can be thought of as a measurement of the gap between current health status and an ideal health situation where the entire population lives to an advanced age, free of disease and disability.” 

Years of life lost is calculated with respect to the average life expectancy at birth. Each disability is given a weight which is multiplied by the years spent living with the disease. E.g. blindness has a disability weight of 0.6, so if you were blind for twenty years that would mean that you have lost 0.6 x 20 = 12 DALYs.

To get the weightings for the disabilities, they brought it to a panel of judges and asked them to give them a weighting from 0 to 1. A weight of 1 meant that they would be indifferent between having the condition and being dead, compared to 0 where one would be indifferent between having the condition and having perfect health. 

Uses

Comparison
It gives a single metric to all of the different diseases, which allows you to find the more cost effective ways to help a population. This helps policy-makers and donors make the difficult decision of who to prioritize with limited resources. 

An important cause
Health is an important cause to focus on. There is much research finding that ill people and countries with high disease burdens are unhappier than their healthier counterparts. 

Additionally, illness is just inherently bad. You have but to recall your own experiences of being ill to confirm this fact. 


Potential flaws

Environmental context
Being blind in Nigeria is worse than being blind in the Netherlands. This is because in the Netherlands there are support systems in place, such as braille and audiobooks. Most of the blind in Nigeria do not get this support. This means that the disability weighting that is assigned to blindness should be different in Nigeria and the Netherlands. However, in the interests of fairness, DALYs are equally weighted everywhere. 

This is not a deal-breaker as all social metrics are slightly flawed.  It is simply something to keep in mind.

Additionally it is still probably the case that treating blindness in Nigeria is a lot less costly than treating blindness in the Netherlands. 


A million spilled lattes
Spilling a latte sucks. You’ve just paid more than you should for a delicious drink and now it’s all wasted. Depending on the severity of your caffeine addiction, you go and buy another one or get on with your day. What a drag. 

However, if I had the choice of preventing a billion lattes being spilled by a billion different people, or saving one single child from dying of malaria, I’d choose the child. And I'm not sure there's any number of lattes that would change my mind

This is because I am a prioritarian. This means I’m like a utilitarian in that I want to maximize happiness and minimize suffering, but with the added rule of prioritizing those less well off. This is because I think that helping the poor is more important than helping the rich, and that helping well-off people while I could be helping the starving seems wrong. 

Again, this does not invalidate DALYs; it just means that you have to be careful when reading findings on them. If you consider yourself a prioritarian, you have to check that the DALYs are helping those who really need your help, not just people in New York who have back pain. 


What about non-health issues?
DALYs do not take into account the pain of social ostracization. For example a cleft lip simply means your face came out a bit wrong and your lip looks bizarre. It can make it slightly harder to eat and talk, but compared to cancer or a heart attack it’s not so bad, so the disability weighting is very small.

What that misses out on is that in many cultures people with cleft lips are ostracized from society. They are not accepted by their family, they are thought to be cursed, and they can find it impossible to make friends or to have their own family. This is devastating. Social isolation is one of the saddest, most lonely things that can happen to a human being. 

This is an important issue about DALYs, however on average you can make a larger difference if you know what you’re doing instead of going forward blindly, and DALYs allow us to see our progress. Unfortunately there isn’t a widely used happiness metric that we can use yet that I know of. (Although please do inform me if there is one.) More on this argument can be read on this excellent article by Adam Casey.