Counting desires

Preference aggregation can be tricky business

A key assumption behind the Global Burden of Disease project is that it is possible to come up with a “Disability Weight” for each health state. ¬†Diseases conditions that are considered worse than other carry higher disability weights than others. ¬†A very important issue in the development of such weights is the question of who should define these conditions? ¬†Should those who have the conditions be the best judge or are they biased? ¬†Should healthy people who have never experienced these conditions be the judge? ¬†Should doctors decide? ¬†Should policy makers? ¬†Should health economists (gasp!!)?

In the past, the GBD has relied upon “expert opinion” to make such decisions. ¬†Well, it seems for the next update of the GBD, which is currently underway, you can also be an expert. ¬†I came across a link to the following survey earlier today that allows you to have some input in these weights.

That’s Karen Grepin discussing an attempt to aggregate beliefs over disease burdens to better define the weights given to different ailments. This is a very similar exercise to preference aggregation, where we attempt to construct a unified set of beliefs that will govern public policy. The result is something approaching a social welfare function, which allows us to make statements like “Society strictly prefers A to B.” One way of doing this is to get a sample of individuals to compare different states and to try and tease out an overall ordinal ranking of these states. Using Grepin’s example, each person has to make a pairwise comparison:

The first person has swelling and tenderness in the testicles and pain during urination.

The second person has lost part of both legs, leaving pain, tingling, and frequent sores in the stumps. The person has great difficulty moving around and has episodes of depression, anxiety and flashbacks to the injury.

By asking enough people to compare different states with different combinations of symptoms, we can tease out their overall ranking of those symptoms – how this is done can sometimes be contentious and quite technical. That ranking then represents the best approximation of everyone’s relative rankings of disease burden.

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