Data from 1.5 million questionnaire respondents has helped researchers narrow personalities into four clusters.
Researchers at Northwestern University found that the four personality types are average, reserved, self-centered and role model—and that over time, people's types can change. Published in the journal Nature Human Behavior on Monday, the study could serve as a useful tool for psychologists or hiring managers and challenges existing systems in the field.
"People have tried to classify personality types since Hippocrates' time, but previous scientific literature has found that to be nonsense," co-author William Revelle, a professor of psychology, said in a statement. "Now, these data show there are higher densities of certain personality types."
Even though Revelle is a co-author on the study, he was skeptical at first. Personality types as a concept are still controversial in psychology, as it can be hard to find scientific proof of types. Other studies used small groups, so scientists have struggled to replicate the results. Revelle challenged the other authors to prove to him that the types existed.
"Personality types only existed in self-help literature and did not have a place in scientific journals," said Luís Amaral, a professor of chemical and biological engineering at Northwestern, said in a statement. "Now, we think this will change because of this study."
The responses were collected through a variety of online personality quizzes that were developed over decades. The quizzes varied between 44 and 300 questions and the results are will be available to other scientists to do their own analysis.
The first personality type is "average." People in the average cluster are described as extroverted and high in neuroticism. Women are more likely to be in this personality type and it's the most common, according to the research. The "reserve" type isn't very extroverted or neurotic. Instead, they're agreeable and conscientious, as well as emotionally stable. Those in both the reserve cluster and the average cluster are not very open.
"Self-centered" people are described as very extroverted and aren't considered very agreeable, conscientious, or open. As people age, the amount of those who fall into the self-centered category declines dramatically in both men and women.
"These are people you don't want to hang out with," Revelle said.
The "role models" type scores high in every trait—extroversion, openness, agreeableness, and conscientious—except neuroticism. People are more likely to be in the Role Model category as they age, and women are more likely to be in this group than men.
"These are people who are dependable and open to new ideas," Amaral said. "These are good people to be in charge of things. In fact, life is easier if you have more dealings with role models."
The scientists also wanted to test how accurate their categories were by defining a group that they felt would overwhelmingly fall into the self-centered category: teenage boys.
"We know teen boys behave in self-centered ways," Amaral said. "If the data were correct and sifted for demographics, they would then turn out to be the biggest cluster of people."
In the self-centered group, teenage boys were overrepresented, while women over the age of 15 were very underrepresented in the group. The scientists felt this showed them their strategy for assigning people to different groups was correct.
Over time, it seemed people become less neurotic and more agreeable and conscientious.
"When we look at large groups of people, it's clear there are trends, that some people may be changing some of these characteristics over time," Amaral said. "This could be a subject of future research."
