Dear DALY: You’re tacky and I hate you

The lovable quote from School of Rock accurately reflects my sentiments of the DALY (disability adjusted life year) and series of Health Metrics in general.

Don’t get me wrong – I believe a system of metrics is quite useful. In theory, they are crucial in keeping a record of health both globally and within our societies. It’s incredibly invaluable to see what exactly is plaguing us today as opposed to a few decades ago. Metrics have the capability of serving as a nice point of reference against which we can determine if anything we’re doing in the public health sector is actually succeeding.

The DALY, while a massive step in the right direction when no alternative was being used, is now sorely obsolete; however, it still remains the standard measurement for the burden of global disease despite decades of backlash for its inaccuracy and misrepresentation.

At its core, the DALY is a numerical value designed to measure the various impacts of disease on people through mortality and morbidity. The potentially healthy years of life lost by diseases are measured, followed by the effects of non-fatal diseases, which are then factored into this ‘black box’ via a disability weight. This weight varies in accordance with an individual’s age – namely, their presumed value to society and position with respect to their ‘peak years of life’.

We can see a massive problem with this metric without having to use too much thought: it necessarily states that the deaths of individuals who are older and/or disabled contribute less to the burden of disease than those of their younger counterparts. This underrepresents diseases and conditions that affect the aging population in more developed countries; and it’s not like we’ve eradicated those afflictions! It’s a significant problem and the DALY, for all intents and purposes, ignores them.

Piggybacking on this notion of misrepresentation, the metrics reported for global health data is wildly inaccurate for most areas of the world that do not contain a vital registration system. Information of deaths and diseases are gathered through surveys and censuses that are incredibly vulnerable to manipulation. If we learned anything from the eight seasons of House, it’s that people lie. They may not even be trying to falsify information – they might simply forget or be unaware of the exact causes of a death in the family. That policy places so much weight on these certainly inaccurate measurements is terrifying. Would you want a physician operating on your body with imperfect knowledge of the actual problem?

Several scholars have made these very criticisms and have even come up with more that are not inherently so obvious. In her section in Reimagining Global Health: An Introduction, Anne Becker and her colleagues bring up two more of these criticisms against the DALY:

The first issue she raises is about the assigned disability weights of diseases. The measurement of disease burden rests on the severity and impact of various diseases, which necessarily relates to the gravity with which we view them. If the top ten most populous countries were suddenly afflicted with a rise in those affected by seasonal allergies, I think it’s safe to say that the world wouldn’t drop everything to find a solution. But that’s just the point: what will elicit such a reaction? What kind of disease and what volume does it need to hit to gain global infamy? The DALY tells us that it should be based on their system of ordering disease severity – one that is wholly arbitrary. A ‘group of independent experts’ is used to determine whether losing an arm is worse than losing a leg. They’re in charge of determining which strain of infection is really worse. While we can argue about the nuances of the science, the final decision is really just a judgement call. There is no indisputable piece of evidence that argues the fine points between what’s number ten on the list of worst diseases and what’s number eleven. Already that undermines the validity of the DALY, which calculates non-fatal diseases against this weighted value to determine global burden.

The darker criticism Becker makes naturally finds itself on the economic side of the debate. According to Becker, the DALY does not account for differences in available resources in a given community. The actual ‘burden’ of diseases and deaths is highly contextual, and will vary rapidly depending on the particular individual and resources of his or her area. While Christopher Murray altruistically defends that a premature death of a person should equally impact the global burden of disease whether he or she was from a developing country or a place like the US, Becker argues that, as unsettling as it is, the deaths are not as alike as we would hope to believe. We like to view ourselves as the apex of human and civil development in a sort of teleological sense of history, but addressing matters on the basis of the idealistic relationships between people may in fact blind us to things we should otherwise be investigating.

The relative burden of a particular disease is highly dependent on who is affected and where they are. It may be useless to keep looking for one catchall metric that will represent everything perfectly. It may instead be more productive to, as Daniel Reidpath puts it in “Measuring health in a vacuum: examining the disability weight of the DALY”, measure burden as it pertains to a particular area. A global, unified measure may not be possible due to the sheer amount of variables that are involved with each individual case.

Any unit of measurement is better than none at all, but an updated method is long overdue. Isn’t it about time we brought health metrics into the 21st century?


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