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Complications with DALYs
There are a number of issues with the DALY framework that are worth bearing in mind. We agree that some of these are concerns. However, it's likely that any solution to them will be a variation on the existing framework. Indeed, it's an advantage of the DALY framework that it makes these concerns explicit; they'd arise regardless of how we made our decisions, it's just that some techniques would gloss over them.
The first is how to deal with future benefits. When given the choice between
1) $100 now
2) $100 in a year’s time (adjusted for inflation)
people normally choose 1) - they'd prefer to get benefits now rather than later.
In the same way, the WHO discounts the value of health far in the future, with a discount factor of 3% a year (compound interest). So this year's health for a ten-year-old child is weighed 3% higher than next year's health for a child who will be ten next year. However, this is much more controversial. There's a very good reason to prefer money now to money later - you could invest the $100 now and end up with more than $100 a year down the line. But this doesn't apply to quality of life; it's not clear why we should privilege people alive now over future people. On the other hand, long-term benefits are more uncertain, so should be discounted when compared to more concrete immediate benefits.
Non-Uniform Age Weighting
The WHO use non-uniform weights for people's wellbeing at different times of their life: DALYs for the very young and very old are worth less than those in the middle.
“Age weighting is a concept unique to the DALY methodology, and is intended to account for the fact that people are supported by others during infancy and at an advanced age, but support others during adulthood. This notion is called welfare interdependence. Welfare interdependence does not imply that the time lived at different ages are more or less important to those individuals, but that the social value is different (14). The age weighting of DALYs therefore accrue more weight to the life years of bread-feeders and care takers, and can be illustrated by a hump-shaped curve which starts at zero for new-borns, peaks at 25, and gradually declines throughout adulthood without ever reaching zero.”1
This is partly because those of working age have had the most human capital invested in them, and also because research suggests we judge deaths in the middle of life as worse than those at the beginning and end. This weighting is highly contentious; DCP2 did not use them, instead valuing DALYs at all stages of life equally.
However, there is still an issue of how to deal with very young children. Historically there has been a discontinuity at birth: saving newborns counted as among the most effective of interventions, as they have the potential to live a very long time. A death just before birth, on the other hand, counts as a stillbirth and receives no weight at all. Even if you think it's appropriate not to place value on unborn children, this discontinuity is concerning. . The DCP2 does list various possible weighting mechanisms, but this is inevitably going to be contentious.
Normative Age Target
DALYs measure how far people's lifespan falls short of a certain length (the 'health gap'), which requires the specification of a 'target' age. As such, they don't count increasing life expectancy to be a benefit, even though preventable deaths are always a tragedy.
For DCP1, target ages of 80 years for men and 82.5 years for women were chosen, which arguably means interventions that help men were undervalued. Then again, doing otherwise could be seen as being biased the other way, and the temporal discounting means that end-of-life effects are likely to be small.
The disability or quality adjustment stage of the metric can be contentious. There are some people who argue that conditions like deafness are not disabilities at all; if so, the 0.8 weighting would unfairly undervalue them.
However, it does seem that interventions to restore sight or hearing are valuable. If they are adding value, being able to see must be more desirable than being blind; the only way to consistently value years of life with disabilities as equally to years of life without them would assign no value to curing or preventing those disabilities. As it seems that becoming blind is undesirable, we stick with the WHO and DCPN's methodology in this respect and do quality-adjustments.
A lot of people want to make a distinction between the deserving and undeserving poor. We might want to discount the second group, valuing more highly assistance to those who are merely unfortunate. QALYs/DALYs don't take this into account, and value both groups equally. However, you might disagree with the relevance of this distinction, and it's unlikely to be an issue when comparing communicable diseases, though it might be more important when comparing charities more widely.
Despite these issues, we still think QALYs/DALYs are the best available tool. They allow us to compare charities working on different interventions. They allow us to compare interventions that save lives to those that improve them, and those that do some of each. They mean we can compare interventions that give many people small benefits to those that give large benefits to a small number of people.
While there are potential problems, many of these are contentious. Some only occur when trying to apply the DALY framework outside of the area they were designed to measure; DALYs weren't intended to measure longevity benefits. If a charity or intervention we were researching had such effects, we'd manually incorporate them into our analysis. Any improvement is likely to be a extension on QALYs/DALYs, rather than a whole new framework. In conclusion then, we think QALYs/DALYs are the right metric to be using.
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