Shortly after the University of Washington announced that the fourth suspected case of the school's new coronavirus had turned out negative, two professors, one in public policy and the other in public health, organized a small dinner for students and teachers.
Like everywhere else on campus, and in much of the world, the coronavirus was everything anyone could talk about.
But one of the participants, a public health student, had had enough. Exasperated, she launched a set of statistics.
The virus has killed around 1 people worldwide and infected around ten in the United States. Alarming, but much more common illness, flu, kills 400 000 people every year, including 34200 Americans last flu season and 61 099 the year before.
Deep uncertainty remains about the death rate from the new coronavirus, with a high-end estimate up to 20 times that of the flu, but some estimates go as low as 0,16% for those affected outside from the overwhelmed Chinese province of Hubei. Roughly on par with the flu.
Wasn't there something strange, asked the student, about the extreme disparity in the reactions of the public?
Ann Bostrom, co-host of public policies for the dinner, laughed as she recounted the evening. The student was right about viruses, but not about people, said Dr. Bostrom, who is an expert in the psychology of how humans assess risk.
Although public health parameters may put the flu next to or even ahead of the new coronavirus for simple death, she says, the mind has its own ways of measuring the danger. And the new coronavirus disease, named COVID-19, hits almost all of the cognitive triggers we have.
This explains the global wave of anxiety.
Of course, it is far from irrational to feel a certain fear that the coronavirus epidemic will spread across China and beyond.
But there is a lesson, say psychologists and public health experts, in the near-terror that the virus induces, even if serious threats like the flu receive little more than a shrug. It illustrates the unconscious biases in how humans perceive risk, as well as the impulses that often guide our responses - sometimes with serious consequences.
How our brains assess the threat
Experts believed that people assessed risk like actuaries, analyzing cost-benefit analyzes whenever a merging car got too close or local crime rates skyrocketed. But a wave of psychological experiences in the 80s upset this thought.
Researchers have discovered that people use a set of mental shortcuts to measure danger. And they tend to do it subconsciously, which means that instinct can play a much more important role than they think.
The world is full of risks, big and small. Ideally, these shortcuts help users determine which ones to worry about and which to ignore. But they can be imperfect.
The coronavirus can be an example.
"It affects all the hot buttons that lead to an increased perception of risk," said Paul Slovic, a psychologist from the University of Oregon who helped pioneer modern risk psychology.
When you meet a potential risk, your brain quickly searches for past experiences with it. If it can easily extract several alarming memories, your brain concludes that the danger is high. But he often fails to assess whether these memories are truly representative.
A classic example is a plane crash.
If two occur quickly, the theft suddenly becomes more frightening - even if your conscious mind knows that these collisions are a statistical aberration with little impact on the safety of your next flight. But if you then take a few flights and nothing goes wrong, your brain will most likely start telling you again that flying is safe.
When it comes to the coronavirus, said Dr. Slovic, it's like people are having a report after which planes have crashed.
"We hear about the deaths," he said. “We don't hear about the 98% or so of people recovering from it and who may have had mild cases. "
This trend can reverse in both directions, leading not to excessive alarm but to excessive complacency. Although the flu kills tens of thousands of Americans each year, most people's experiences with it are relatively mundane.
Knowing how dangerous the flu is does not change that, studies show. The brain risk assessment approach simply goes beyond rational calculation - a source of endless dismay for health officials who are trying to increase flu vaccination rates.
"We are conditioned by our experiences," said Dr. Slovic. "But experience can mislead us to be too comfortable with things. "
Bias, shortcuts and intestinal instincts
The coronavirus also uses other psychological shortcuts to assess the risk.
One involves novelty: we are conditioned to focus strongly on new threats, looking for any cause for alarm. This can lead us to be obsessed with the scariest reports and worst case scenarios, making the danger even greater.
Perhaps the most powerful shortcut of all is emotion.
It is extremely difficult to assess the danger posed by the coronavirus; even scientists are not sure. But our brains act as if they had a simpler way: they translate intestinal emotional reactions into what we think are reasoned conclusions, even if solid data tells us otherwise.
"The world in our heads is not an exact replica of reality," wrote Daniel Kahneman, Nobel Prize-winning economist, in a book from 2011. "Our expectations regarding the frequency of events are distorted by the prevalence and emotional intensity of the messages to which we are exposed."
In extreme cases, this can lead to a “crowding out effect,” said Dr. Bostrom, because our emotional impulses overwhelm our cognitive faculties. The coronavirus strikes a number of these triggers, often quite hard.
One is scary.
If a risk seems particularly painful or disturbing, people tend to increase their estimate of the probability of it happening to them. Coronavirus reports often present overwhelming images: unhygienic food markets, city-wide closures, and overcrowded hospitals.
Another trigger is a threat that is not fully understood. The less known it is, the more people can fear it and overestimate its threat.
Uncontrolled threats, such as an uncontrollable disease outbreak, provoke a similar response, leading people to look for ways to re-impose control, such as hoarding supplies.
The risks that we take voluntarily, or that at least feel voluntary, are often considered to be less dangerous than they really are. One study found that people will increase their danger threshold they are willing to take by a factor of a thousand if they consider the risk to be voluntary.
If this number seems high, consider that driving, a danger that most take voluntarily, kills over 40 000 Americans every year. But terrorism, a threat imposed on us, kills less than 100 people.
There are countless rational reasons why terrorism provokes a sharper response than deaths from traffic accidents. The same is true for an epidemic that spreads quickly and is poorly understood compared to the common flu.
And that's exactly the point, say psychologists.
"All of these things affect our feelings," said Dr. Slovic. "And this is the representation of the threat to us. Not the risk statistics, but the feelings of risk. "
To make choices
All of these emotions can have real consequences.
Consider the response to the partial collapse of the Three Mile Island nuclear power plant in Pennsylvania in 1979. Although the incident was not fatal, it led to public demand for nuclear power fossil fuels including impact on air qualityalone would cause thousands of premature deaths each year.
This calculation confounded the economists of the old school, who considered it irrational. A leading nuclear energy specialist called him "crazy."
But it has also helped give birth to new psychological models of how people measure risk.
"Our feelings don't do arithmetic very well," said Dr. Slovic.
This may be especially true when judging low probability and high risk threats like nuclear war, terrorism - or dying from the coronavirus or the flu.
Our minds tend to "round" the probability to "fundamentally zero" and we under-react, said Dr. Slovic. Or we focus on the worst case, he said, which "gives us a strong feeling, so we overreact. "
This article appeared first (in English) on NEW YORK TIMES