Mar 5, 2021

Poor Risk Analogies

In making their arguments for/against COVID-19 mitigation strategies, people often use risk analogies. However, these analogies are often premised on a flawed conception of COVID risk. Here's a typical example from a wise health expert I really like:

In Zero Covid, the goal is to reduce the number of COVID-19 cases to the lowest level possible—seemingly regardless of the consequences of that approach.

In Harm Reduction, the goal is to reduce the harm caused by COVID-19 across all domains: physical, mental and emotional, economic, social, etc.

Let me use an analogy to explain the difference. We have about 40,000 traffic fatalities in the United States each year. These are tragic, and technically preventable, deaths. If we lowered the speed limit to 5 mph—even on the highway—we could likely reduce the number of traffic deaths to a small handful, if not zero. This would be analogous to a Zero Covid strategy.

But if we did that, our society (as we know it) would come to a grinding halt. It would take you three hours to get to work, or the grocery store, or to pick up your kids from school. Food would rot in trucks on the highway. Obviously, this is not the path we took. Instead, we’ve chosen to set higher speed limits, knowing that they will, unfortunately, contribute to a not insignificant number of deaths each year. We’ve decided that the benefits of having a functional society outweigh the costs of these fatalities. This is a Harm Reduction strategy ...

Most of us don’t think about this each time we get into a vehicle. We don’t consider the trade-off that we’ve made as a society, nor do we consciously consider the risk-reward calculation that each of us is making (i.e., the small chance that we could be seriously harmed or killed in a traffic accident on the way to the grocery store). We are so familiar with this risk that we don’t even think about it anymore.

(Source: "Should we isolate kids who were exposed to COVID-19?" email by Chris Kresser)

I agree with Kresser that Harm Reduction is the correct strategy for Covid and that Zero Covid ignores too many other variables — what Libertarians call "the seen vs. the unseen."

However, for the car-accident analogy to be correct, such an accident would have to cause 1.4 to 3.9 other people (source: Medscape) to go and have a car accident, who each would cause 1.4 to 3.9 other people to have a car accident, and so on.

To torture the analogy, maybe most of those accidents would be minor fender-benders or even just light taps resulting in no damage. But elderly drivers (because of poor vision and delayed reflexes) would tend to have fatal accidents more often. Etc.

(N.B. It was Nassim Taleb who first helped me understand this.)