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A few years ago, Jason Rentfrow, a psychologist at the University of Cambridge, dug into a question that has captivated him for decades: Do different places have different personalities? Do people in Los Angeles, for instance, have measurably different temperaments from the residents of Augusta, Georgia? If so, what does that mean for both places? Rentfrow decided to test these questions on a phenomenon that has captivated all of America lately: the rise of Donald Trump.

Together with his co-authors, Rentfrow analyzed a set of surveys that had been conducted from 2003 to 2015 in 2,082 U.S. counties—about two-thirds of all the counties in the country. The surveys asked 3 million people 44 questions about their habits and dispositions. Rentfrow and his co-authors focused on neuroticism, a tendency to feel depressed or anxious and to respond more severely to stress. Neuroticism is one of the “big five” traits that psychologists often use to measure personality. The study authors compared each county’s level of neuroticism with whether those counties later voted for Trump in the 2016 election, and whether they had historically voted for Republicans.

It turned out that neuroticism was indeed correlated with support for Trump. This was true even when controlling for each population’s racial makeup, education level, income, and political attitudes. In fact, neuroticism was strongly linked to the margin by which Trump outperformed the 2012 Republican nominee, Mitt Romney. The same pattern held with Brexit votes, the study also found: The more neuroticism in a given area of the United Kingdom, the more likely people were to support the country leaving the European Union.

Based on this correlation, Rentfrow and his co-authors speculate that neuroticism is a force that attracts people to populist candidates and ideas. The more people in a certain region tend to worry, the authors posit, the more politicians can tap into those worries and drum up support for their populist messages. Trump, for instance, stoked voters’ fears about immigrants, terrorists, and other interlopers. Neuroticism particularly seemed to drive a shift toward Trump support in Pennsylvania, Wisconsin, and Ohio, the authors write—states that were thought to be crucial to Trump’s 2016 victory.

This study and the other work by Rentfrow and many of his colleagues have added some scientific basis to the common inkling that people in different parts of the United States act differently. There are already many stereotypes: New Yorkers are always in a hurry; Californians are extremely chill; Minnesotans are unusually nice. While these sorts of characteristics don’t apply to every person in an area, Rentfrow and his cohort quantified some of the personality differences that do exist among states. The effort could ultimately help Americans understand themselves a little better.

Rentfrow acknowledges that his approach can be controversial. People rarely like to hear generalizations about their hometown, especially if the generalization is that it’s an unusually neurotic place. And of course, many factors influence voting behaviors aside from personality. “Psychology is about trying to understand the inner workings of people’s minds,” he told me. “Here I was trying to make these broad generalizations, not just about individuals, but about people based on where they lived.”

Rentfrow had a breakthrough in 2013, when he and others published a study that suggested the U.S. has three “psychological regions.” The first, in the Midwest and parts of the Southeast, is “friendly and conventional.” It has high levels of extroversion, agreeableness, and conscientiousness—three more of the big-five personality traits. “The characteristics of this psychological region suggest a place where traditional values, family, and the status quo are important,” the authors wrote. (The southern United States also tends to be more courageous, according to his research.)

Rentfrow et al., Personality Processes and Individual Differences

In a second region, which consists of the West Coast, the Rocky Mountains, and the Southwest, meanwhile, Americans tend to be “relaxed and creative,” the authors wrote. People in these areas are very open—another big personality measure, marked by a tendency toward curiosity, variety, and imagination—but rank comparatively low on most all other traits. “In general, the qualities of this region depict a place where open-mindedness, tolerance, individualism, and happiness are valued,” the authors noted.

REntfrow et al., Personality Processes and Individual Differences

Finally, there’s the “temperamental and uninhibited” region, which consists of the Northeast and, to some extent, Texas. These states have higher neuroticism than the others and are moderately high on openness. “This particular configuration of traits depicts the type of person who is reserved, aloof, impulsive, irritable, and inquisitive,” he wrote. To which we on the East Coast say, You talkin’ to me?

REntfrow et al., Personality Processes and Individual Differences

Personality might clump up in this way for a few reasons. The neuroticism belt, for example, might have come about because many East Coast cities tend to be old and crowded, and living in such an environment can contribute to anxiety—as anyone who has ridden a packed subway car at rush hour can attest. Neuroticism also happens to be higher in areas that have been dominated—and since abandoned—by coal-based industries, suggesting that economic woes can eviscerate mood. And compared with the sunny West Coast, in the chilly, swampy east, “the weather, in general, may not be quite as nice,” Rentfrow told me.

Of course, in Rentfrow’s study about the 2016 election, neuroticism was associated with Trump support, whereas the supposedly neurotic Northeast was one of the few regions where the Democratic candidate, Hillary Clinton, won states. But at a county level, Trump still dominated many places in the Northeast, and neuroticism might explain why he was more popular than Romney in those areas.

Openness, meanwhile, is highest in large, cosmopolitan cities. The states that are high in openness, therefore, tend to be those that have large cities. There’s also some evidence that agreeableness—kindness and warmth—clusters toward the southern United States and the northern Great Plains. Perhaps that’s because people there don’t tend to move as much, Rentfrow said, and thus forge more lasting relationships with their neighbors.

Some of this process is a feedback loop from the environment: People in high-crime neighborhoods might grow to be cautious and skeptical, because if they are too trusting, they risk becoming victims. Another mechanism is selective migration, or the tendency of people to move to areas that might satisfy their needs or interests. Live-music junkies, for example, might flock to Austin or Nashville.

Finally, there’s the so-called ecological influence, or the qualities of the natural world that surrounds us. Living near the beach might influence how much time you spend outside, how much you value physical appearance, and what your hobbies are—all factors that can then shape your personality. In one of Rentfrow’s studies, people in both China and the U.S. who grew up in areas that were close to 72 degrees Fahrenheit were found to be more agreeable, conscientious, and emotionally stable.

Living in a certain state won’t completely rearrange someone’s personality, or even necessarily have much of an effect. Individual personalities are, in part, genetically determined: If you have two very gregarious parents, you’ll probably have at least a little extrovert in you. But your environment can nudge your personality in a certain direction.

“Your genetics determines your range,” says Sam Gosling, a psychologist at the University of Texas who has worked with Rentfrow on many studies. On a 10-point scale, your biology might set you between a two and a five on openness, but your environment and other circumstances will determine whether you’re closer to the two or the five. “Even if you’re genetically low on openness but you live in New York City, you’re going to be exposed to a huge variety of ideas, different types of people, food, art, and culture,” Gosling says. “You’ll be toward the top of your biological range.”

Despite how many studies Rentfrow and others have now produced, there are still some reasons to be cautious about this research. For one, the impulse to psychoanalyze large groups of people has a dark history. After World War II, some psychologists speculated that fascists had a specific personality that enabled them to commit the atrocities of the Holocaust. Some even proposed now-debunked ideas about how harsh parenting or latent homosexuality could lead to Nazism. Today, studies like Rentfrow’s are conducted with more empirical care—and with the knowledge that even if a lot of neurotic people live in a place, it won’t mean that every single resident has a Lexapro prescription. Averages are averages, but individuals are all distinct.

Plus, people both shape and are shaped by their environments. It’s impossible to know whether California causes people to be relaxed, for example, or if relaxed people move to California—and in fact, it’s probably a little of both. “We can’t randomly assign people to Alabama versus Minnesota,” Shigehiro Oishi, a psychologist at Columbia University, told me.

Still, if these findings hold up, they hold important ramifications for politics and policy. They could, for instance, help policy makers better tailor resources and programs to spur economic growth or promote healthy eating. In one of the studies from Rentfrow and researchers at the University of California at Davis, low conscientiousness—a tendency to be less responsible and less self-controlled—predicted worse health and more substance use. Rentfrow and others have also found that areas low in neuroticism and high in openness, extroversion, and conscientiousness tend to have more robust economies.

On a more fundamental level, understanding the psychology of places helps us understand what we talk about when we talk about regional differences. Why do some areas have such high rates of obesity or heart disease? Why do some states seem to weather recessions better than others? Why do some cities become lively hubs of beer and bachelorettes while others wither and die out? “All of those things are essentially the consequence of people doing something rather than something else,” Gosling says. And what people do, in turn, depends in part on their personality.

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