People Who Don't Wear Masks Misunderstand Coronavirus Spread

Wearing masks and social distancing have been shown the be the most important measures we can take to fight coronavirus. Yet a large number of people don’t see the need, leading to recent surges in most U.S. states. A new study shows that people who aren’t wearing masks misunderstand how Covid-19 spreads.

Researchers at the Social Cognition Center Cologne and the University of Bremen conducted three experiments, each involving more than 500 adults from the United States. A sizable number of them did not see the point of social distancing or mask-wearing because they made a simple mistake about statistics. People tend to think coronavirus spreads linearly when it really spreads exponentially.

Exponential growth is how coronavirus spreads

Source: Wikipedia/Public Domain.

Linear vs. exponential

What’s the difference between linear and exponential spread? The answer makes all the difference in the world. Linear growth goes up in a measurable and, well, linear way. But exponential growth is rapidly additive: It multiplies itself by itself.

The study authors referred to the difficulty people have understanding this as the exponential growth bias. “In general, people have difficulty understanding exponential growth and erroneously interpret it in linear terms instead,” explains first author Joris Lammers in a press release. When people don’t understand, they massively underestimate how fast coronavirus spreads. Likewise, they also underestimate how big a difference social distancing makes for stopping the spread.

The paper reported three studies, which ran toward the end of March 2020 when coronavirus was spreading rapidly in the United States. The first looked at how participants understood viral spread. It showed that many Americans mistakenly understood the virus’s growth in linear terms, even when presented with evidence that it was exponential. Political orientation mattered; conservatives were more likely to misunderstand exponential growth than liberals.

Social distancing makes sense when we understand viral growth

Prior research has shown that the exponential growth bias is hard to overcome, but this report found differently. In the second study, researchers gave one group of participants the following instructions:

“Please keep in mind that many people forget that the speed by which the coronavirus spreads, increases each day. In other words, when making these guesses, many people erroneously think that the coronavirus cases have increased at a steady and constant pace. In reality, in the USA (as in almost all other countries) the number of corona patients doubles and keeps doubling every three days.”

When compared to the control group, which had not been given these instructions, the group that was taught about exponential spread was much more likely to support social distancing.

A third study had the experiment group use what they were taught about exponential growth to create multiple predictions of coronavirus case counts over time. When they saw just how fast the virus spread over time, participants felt even more support for wearing masks and social distancing.

We have a tremendous opportunity to slow or even halt the coronavirus pandemic by wearing masks and social distancing. But we are only going to do it if we understand the reason why.

This article was originally published at Forbes.com.