(2022-02-04) Johnson We Need A Standard Unit Of Measure For Risk

Steven Johnson: We Need A Standard Unit Of Measure For Risk. “The average weekly chance that a boosted person died of Covid was about one in a million during October and November… That risk is not zero, but it is not far from it. The chance that an average American will die in a car crash this week is significantly higher—about 2.4 per million.” There was a flurry of controversy last week about David Leonhardt’s “The Morning” newsletter in the Times

Our problems with making risk assessments are manifold, and there are many terrific books out there on the ways probability thinking messes with our intuitive understanding of the world. Tim Harford (who has written one of those books himself) had a very helpful rundown of them on Twitter a few days ago.

One problem we have is that risk is usually both relative and cumulative in nature.

Another problem with risk is that it often revolves around very small probabilities, which can lead to all sorts of base-rate confusion

A few decades ago the Stanford professor Ronald Howard proposed a unit of measure for mortality risk. He called it the “micromort.”

There was an op-ed in the Times in May of 2020 that discussed COVID risk using the language of micromorts. The Wharton School professor Ethan Mollick posted a short thread on Twitter last summer discussing the ways vaccines reduced your COVID risk, using Howard’s unit of measure:

The one problem I have with the concept—which is a problem intrinsic to these kinds of risk assessments generally—is that we don’t have an intuitive understanding of very small probabilities

you want it to be anchored in something intelligible

I think a much better unit of measure is the one that Leonhardt employed in his column last week: the risk of dying in an automobile crash... The convenient thing about using the automobile framing is that a two-hour trip at mostly highway speeds happens to come out almost exactly to a one-in-a-million chance of dying.

I did some rough calculations on the NYC COVID data, and came out with the estimate that just going about your normal business in New York City during the first week of March 2020—before the lockdowns kicked in—was 625 micromorts

During the pre-Omicron days in the fall of 2021, hanging out in NY for a week was about 10 micromorts. If you were a healthy vaccinated person, your risks were indeed—as Leonhardt suggested—likely lower than taking a road trip for a few hours.

The height of the Omicron wave last week brought that number up to 80 micromorts. Not terrifying, but certainly reason to buckle up for a month or two.

I will still be interested to know if the flu risk starts to climb in New York, even by a few micromorts—I wouldn’t radically change my plans, but I might put on a mask in the subway for a few weeks

For the past seventy years, every single local news broadcast has been telling you what the temperature is going to be tomorrow, and the chance of precipitation. Why shouldn’t they also include genuinely life-or-death odds? Basically, risk weather: “The next week looks like we will be reaching a high of 50 micromorts, thanks to the new variant—though only about 8 micromorts if you’re vaccinated. For seniors, though, we’ll probably see a high in the 100s, so you might want to cut back on socializing indoors.”

And of course a standardized way of describing risk would allow us to debate—and formalize—a set of thresholds for relaxing public health interventions: mask mandates or restaurant vaccination restrictions could be pegged to a specific micromort level.

Risk assessment is undoubtedly trickier with epidemics because a unit of measurement like the micromort is fundamentally personal in nature

Epidemics are by definition social phenomena (public health) and they involve evolutionary forces that shift over time. You may personally not face much risk right now, but by exposing yourself to the virus, you give it a chance to continue a chain of replication that might lead to a new, more deadly variant, or infect an immunocompromised person.

But I think there’s a strong case to be made that having some kind of standardized unit to describe risk would be far preferable to the vague, unanchored way we talk about it today.