Daniel Gardner - The Science of Fear

But if you stop and think about it, that makes no sense. How can it be more likely that Linda is a bank teller and a feminist than that she is solely a bank teller? If it turns out to be true that she is a bank teller and a feminist, then she is a bank teller—so the two descriptions have to be, at a minimum, equally likely. What’s more, there is always the possibility that Linda is a bank teller but not a feminist. So it has to be true that it is more likely that she is a bank teller alone than that she is a bank teller and a feminist. It’s simple logic—but very few people see it.

So Kahneman and Tversky stripped the quiz down and tried again. They had students read the same profile of Linda. But then they simply asked whether it is more likely that Linda is (a) a bank teller or (b) a bank teller who is active in the feminist movement?

Here, the logic is laid bare. Kahneman and Tversky were sure people would spot it and correct their intuition. But they were wrong. Almost exactly the same percentage of students—85 percent—said it is more likely that Linda is a bank teller and a feminist than a bank teller only.

Kahneman and Tversky also put both versions of the “Linda problem,” as they called it, under the noses of experts trained in logic and statistics. When the experts answered the original question, with its long list of distracting details, they got it just as wrong as the undergraduates. But when they were given the two-line version, it was as if someone had elbowed them in the ribs. Head stepped in to correct Gut and the error rate plunged. When the scientist and essayist Stephen Jay Gould took the test, he realized what logic—his Head—told him was the right answer. But that didn’t change what intuition—his Gut—insisted was true. “I know [the right answer],” he recounted, “yet a little homunculus in my head continues to jump up and down, shouting at me—‘but she can’t just be a bank teller; read the description. ’”

What’s happening here is simple and powerful. One tool Gut uses to make judgments is the Rule of Typical Things. The typical summer day is hot and sunny, so how likely is a particular summer day to be hot and sunny? Very. That’s a simple example based on a simple notion of what’s “typical,” but we are capable of forming very complex images of typicality— such as that of a “typical” feminist or a “typical” bank teller. We make these sorts of judgments all the time and we’re scarcely aware of them for the good reason that they usually work, and that makes the Rule of Typical Things an effective way to simplify complex situations and come up with reliable snap judgments.

Or at least, it usually is. The Linda problem demonstrates one way the Rule of Typical Things can go wrong. When there’s something “typical” involved, our intuition is triggered. It just feels right. And as always with intuitive feelings, we tend to go with them even when doing so flies in the face of logic and evidence. It’s not just ordinary people who fall into this trap, incidentally. When Kahneman and Tversky asked a group of doctors to judge probabilities in a medical situation, the Rule of Typical Things kicked in and most of the doctors chose intuition over logic.

Another problem is that the Rule of Typical Things is only as good as our knowledge of what is “typical.” One belief about typicality that is unfortunately common in Western countries, particularly the United States, involves black men: The typical black man is a criminal and the typical criminal is a black man. Some people believe this consciously. Others who consciously reject this stereotype nonetheless believe it unconsciously—as even many black men do. Imagine someone who believes this—consciously or not—walking down a city sidewalk. A black man approaches. Instantaneously, this person’s Gut will use the Rule of Typical Things to conclude that there is a good chance this black man is a criminal. If Head does not intervene, the person will experience anxiety and consider crossing the street. But even if Head does put a stop to this nonsense, that nagging worry will remain—which may produce the uneasy body language black men so often encounter on sidewalks.

There’s another big downside to the Rule of Typical Things, one that is particularly important to how we judge risks. In 1982, Kahneman and Tversky flew to Istanbul, Turkey, to attend the Second International Congress on Forecasting. This was no ordinary gathering. The participants were all experts—from universities, governments, and corporations—whose job was assessing current trends and peering into the future. If anyone could be expected to judge the chances of things happening rationally, it was this bunch.

The psychologists gave a version of the “Linda problem” to two groups, totaling 115 experts. The first group was asked to evaluate the probability of “a complete suspension of diplomatic relations between the USA and the Soviet Union, sometime in 1983.” The second group was asked how likely it was that there would be “a Russian invasion of Poland, and a complete suspension of diplomatic relations between the USA and Poland, sometime in 1983.”

Logically, the first scenario has to be more likely than the second scenario. And yet the experts’ ratings were exactly the opposite. Both scenarios were considered unlikely, but the suspension-following-invasion scenario was judged to be three times more likely than the suspension scenario. A Soviet invasion of Poland was “typical” Soviet behavior. It fit, in the same way “active feminist” fit with Linda’s profile. And that fit heavily influenced the experts’ assessment of the whole scenario.

Many other studies produced similar results. Kahneman and Tversky divided a group of 245 undergrads at the University of British Columbia in half and asked one group to estimate the probability of “a massive flood somewhere in North America in 1983, in which more than 1,000 people drown.” The second group was asked about “an earthquake in California sometime in 1983, causing a flood in which more than 1,000 people drown.” Once again, the second scenario logically has to be less likely than the first, but people rated it one-third more likely than the first. Nothing says “California” quite like “earthquake.”

As Kahneman and Tversky later wrote, the Rule of Typical Things “generally favors outcomes that make good stories or good hypotheses. The conjunction ‘feminist bank teller’ is a better hypothesis about Linda than ‘bank teller,’ and the scenario of a Russian invasion of Poland followed by a diplomatic crisis makes a better narrative than ‘diplomatic crisis.’ ” Gut is a sucker for a good story.

To see the problem with this, open any newspaper. They’re filled with experts telling stories about what will happen in the future, and these predictions have a terrible track record. Brill’s Content , a sadly defunct magazine that covered the media, had a feature that tracked the accuracy of simple, one-off predictions (“Senator Smith will win the Democratic nomination”) made by famous American pundits like George Will and Sam Donaldson. The magazine compared their results to those of a prognosticator by the name of "Chippy,” a four-year-old chimpanzee who made predictions by choosing among flash cards. Chippy was good. While the average pundit got about 50 percent of his or her predictions right—as good as a flipped coin—Chippy scored an impressive 58 percent.

Of course, pundits don’t limit their futurology to simple predictions. They often lay out elaborate scenarios explaining how Senator Smith will take the Democratic nomination and the presidential election that follows, or how unrest in Lebanon could produce a long chain reaction that will lead to war between Sunni and Shia across the Middle East, or how the Chinese refusal to devalue the currency could send one domino crashing into the next until housing prices collapse in the United States and the global economy tips into economic recession. Logically, for these predictions to come true, each and every link in the chain must happen—and given the pundits’ dismal record with simple one-off predictions, the odds of that happening are probably lower than Chippy’s chances of becoming president.