House Majority Leader Cantor’s loss has produced a national “availability cascade.” Photographer: Alex Wong/Getty Images
House Majority Leader Cantor’s loss has produced a national “availability cascade.” Photographer: Alex Wong/Getty Images

House Majority Leader Eric Cantor’s loss to David Brat in the Virginia Republican primary has produced a national “availability cascade.” This is a process of belief formation through which a single event becomes widely known, is taken to reveal some broader pattern or truth, and produces a large-scale change in people’s judgments about probability. Like many availability cascades, this one may well lead to big mistakes.

For mainstream politicians in the Republican Party, the post-Cantor cascade is likely to produce far more fear of the Tea Party than reality warrants -- with unjustified effects on American politics and voting patterns in Congress.

To see the point, we need to step back a bit. How do people form beliefs about probability? In the early 1970s, psychologists Daniel Kahneman and Amos Tversky argued that people use heuristics, or mental shortcuts. One of their principal examples was the “availability heuristic”: People’s estimates of probability reflect “the ease with which instances or associations could be brought to mind.”

Consider, for example, the following question: In the English language, is the letter “n” more often the first letter of a word, or the third letter? People tend to think it's more often the first letter. But that’s wrong. People make the mistake because it’s easy to think of a lot of words that start with “n,” but it takes some work to think of those with “n” in the third position. That is, words that begin with “n” are more available to the mind.

The availability heuristic much affects our judgments about risks. Murders are highly publicized, so people tend to believe that more people die from homicide than from suicide -- when in fact the opposite is true. People also underestimate the number of deaths from quiet killers such as strokes and diabetes. In the electoral context, Kahneman and Tversky specifically noted that “one may evaluate the probability that a politician will lose an election by considering various ways in which he may lose support.”

The availability heuristic influences not merely our beliefs, but our behavior, too. If floods have not occurred in the recent past, people who live on flood plains are far less likely to buy insurance. In the immediate aftermath of an earthquake, there is an increase in the percentage of people who buy insurance against earthquakes -- but the percentage steadily falls from that point, as vivid memories recede.

Which ideas are available to the mind depends, of course, on what people are discussing. If it is headline news, a single violent crime, for example, can make a community a lot more fearful than reality warrants. If it goes viral on social media, a harmful release of toxic waste can make people overestimate the risks associated with toxic wastes. A well-publicized train crash can give people the false impression that it's unsafe to travel by train. Terrorists hope to create availability cascades, giving people the impression that they “cannot be safe anywhere.” The more people who join an availability cascade, the more its force is amplified.

Turn to Cantor’s defeat. Notwithstanding that outcome, recent months have gone poorly for the Tea Party, with significant victories by establishment incumbents Senators Lindsey Graham in South Carolina and Mitch McConnell in Kentucky, and prominent Tea Party losses in Pennsylvania, Georgia, Oregon and Idaho. But Cantor’s defeat is far more available than any of those outcomes. Now Republican politicians don’t want to be “another Eric Cantor,” and many of them will campaign, and vote, accordingly.

Kahneman and Tversky emphasized that while the availability heuristic generally works pretty well, it can lead to severe and systematic errors. They were particularly concerned with biased judgments, produced by “the retrievability of instances.” Of course it is true that other incumbent Republicans may be vulnerable to Tea Party candidates; Mississippi Senator Thad Cochran, for example, is facing a serious challenge from Chris McDaniel. But for the most part, mainstream Republicans would probably be wise to see Cantor’s loss as a product of highly unusual circumstances in a single district, not as significant evidence of the Tea Party's general appeal.

But many will not. An availability cascade makes people overreact, especially when their political futures are on the line.

To contact the writer of this article: Cass R. Sunstein at csunstei@law.harvard.edu.

To contact the editor responsible for this article: Mary Duenwald at mduenwald@bloomberg.net.