Probability Judgments

Julia Marcus, an epidemiologist at Harvard Medical School, was on a recent episode of the Ezra Klein show to discuss thinking about personal risk during the COVID-19 Pandemic. Klein and Marcus talked about the ways in which the United States Government has failed to help provide people with structures for thinking about risk, and how this has pushed risk decisions onto individuals. They talked about how this creates pressures on each of us to determine what activities are worthwhile, what is too risky for us, and how we can know if there is a high probability of infection in one setting relative to another.


On the podcast they acknowledged what Daniel Kahneman writes about in his book Thinking Fast and Slow – humans are not very good at making probability judgments. Risk is all about probability. It is fraught with uncertainty, with with small likelihoods of very bad outcomes, and with conflicting opinions and desires. Our minds, especially our normal operating mode of quick associations and judgments, doesn’t have the capacity to think statistically in the way that is necessary to make good probability judgments.


When we try to think statistically, we often turn to substitutions, as Kahneman explains in his book. “We asked ourselves how people manage to make judgments of probability without knowing precisely what probability is. We concluded that people must somehow simplify that impossible task and we set out to find how they do it. Our answer was that when called upon to judge probability, people actually judge something else and believe they have judged probability.”


This is very important when we think about our actions, and the actions of others, during this pandemic. We know it is risky to have family dinners with our loved ones, and we ask ourselves if it is too risky to get together with our parents, with siblings who are at risk due to health conditions, and if we shouldn’t be in the same room with a family member who is a practicing medical professional. But in the end, we answer a different question. We ask how much we miss our parents, if we think it is important to be close to our family, and if we really really want some of mom’s famous pecan pie.


As Klein and Marcus say during the podcast, it is a lot easier to be angry at people at a beach than to make probability judgments about a small family dinner. When governments, public health officials, and employers fail to establish systems to help us navigate the risk, we place the responsibility back onto individuals, so that we can have someone to blame, some sense of control, and an outlet for the frustrations that arise when our mind can’t process probability. We distort probability judgments and ask more symbolic questions about social cohesion, family love, and isolation. The answer to our challenges would be better and more responsive institutions and structures to manage risk and mediate probability judgments. The individual human mind can only substitute easier questions for complex probability judgments, and it needs visual aids, better structures, and guidance to help think through risk and probability in an accurate and reasonable manner.

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