Disability Weighting

A year or so back, I was having a discussion with a non-economics student about some difficulties in doing benefit-cost analysis, because it can be hard to put values on some outcomes.

The student listened to me patiently, and then said: “Well, it’s not like you have to put values on everything.”

And I thought: That feeling is one of the fundamental differences between economists and non-economists. When there are both benefits and costs, and choices about how to proceed, we as individuals and as a society do in fact put values on everything. These values may in many cases be implicit. We don’t explicitly say what it’s worth in dollar terms to, say, make a highway off-ramp safer or to raise the math test scores in an elementary school by a certain amount. But in making decisions about what to do, or not to do, our values are expressed nonetheless. And then economists come along and try to estimate these values explicitly, which can make non-economists deeply uncomfortable.

For an example of explicit weights in an area where noneconomists would be tempted to say “you don’t need to put a number on everything,” consider the “disability weights” from the Global Burden of Disease study produced by the  Institute for Health Metrics and Evaluation (based at the University of Washington, but with research collaborators around the world). To evaluate health outcomes, trends, and policies, it’s clearly not enough just to measure lives lost or life expectancy. One also needs to account for costs of disability and sickness. Thus, the project uses “disability weights:”

Disability weights, which represent the magnitude of health loss associated with specific health outcomes, are used to calculate years lived with disability (YLD) for these outcomes in a given population. The weights are measured on a scale from 0 to 1, where 0 equals a state of full health and 1 equals death. This table provides disability weights for the 440 health states (including combined health states) used to estimate nonfatal health outcomes for the GBD 2021 study.

You can download the full “disability weights” table using data for 2021 here (with free registration). But for example on the scale from zero (perfect health) to one (death), mild diarrhea (three times a day, with some intestinal discomfort) has a weight of .07. Moderate diarrhea (more than three times a day, with severe belly cramps) has a weight of .18. Severe diarrhea (more than three times a day, severe belly cramps, nausea, and thirst) has a weight of .24.

Or as another example, mild early syphilis (low fever) has a weight of .005. However, severe disfigurement, neurological and cardiovascular problem from adult tertiary syphilis has a weight of .54.

Or as one more example, mild Alzheimer’s disease and other dementia (some trouble remembering recent events, hard to concentrate) has a weight of .06. Moderate Alzheimer’s (memory problems, disoriented, needs help with some daily activities) has a weight of .37. Severe Alzheimer’s (complete memory loss, no longer recognizes family members, needs help with all daily activities) has a weight of .44.

Obviously, one can ask questions about where these weights come from and disagree with them. The Global Burden of Disease website has background to try to persuade you that their choices are least reasonable ones, given the inevitable range of uncertainty.

You may also feel a degree of discomfort that isn’t just about the accuracy of these numbers, but about whether it is either unsuitable or impossible to estimate disability weights at all. But remember, how we (as individuals or as a society) think about health trends, as well as what health-related policies we prioritize, or don’t, is based in part on our own disability weights–whether we like putting a number on it or not.