New study reveals four major personality types

As early as Hippocrates’ time, people have pondered on the best way to classify personalities. In fact, Hippocrates came up with one of the oldest personality type systems in the world, where he defined four personality types based on a person’s “humor” or the proportion of bodily fluids in one’s body. The predominant form of fluid determines the person’s appearance, behavior and psychological type.

In Hippocrates’ words, the four personality types, or “temperaments,” are: sanguine, choleric, melancholic and phlegmatic. The sanguine personality type is characterized by blood and represents social usefulness; the choleric type is characterized by extroversion; the melancholic type is characterized by an analytical and detail-oriented presentation; and the phlegmatic type is indicative of a relaxed and easygoing presentation.

Although no solid relationship exists between internal secretions and human behaviors, people have passed down Hippocrates’ initial outlook on personality for centuries and it is still currently adopted by a few personality type systems. In the period between Hippocrates’ time and modern times, people have developed numerous other personality type systems in attempts to accurately capture the scope of the human mind.

Recently, after sifting through more than 1.5 million questionnaires from around the world, researchers at Northwestern University have reached a new conclusion about four distinct clusters of personality types: average, reserved, self-centered and role model.

Luís Amaral, a professor of Chemical and Biomolecular Engineering at the McCormick School of Engineering at Northwestern University, led the research team.

William Revelle, professor of Psychology in the Weinberg College of Arts and Sciences and a co-author of the study, reveals that he was initially uncertain about the practicality of the study. Personality type is an abstract concept, and scientific evidence in the field has always been hard to come by. 

In fact, most research efforts in personality types are rarely published in scientific journals. However, this new study will be published in the journal Nature Human Behavior, and it might serve as a trailblazer in the field.

The research team designed the online questionnaires by developing them over a longitudinal period of time. Other members of the research community have viewed the data for further analyses.

“The data came back, and they kept coming up with the same four clusters of higher density, and at higher densities than you’d expect by chance, and you can show by replication that this is statistically unlikely,” Revelle said in a press release.

Amaral also shared his insight into the study.

“The thing that is really, really cool is that a study with a dataset this large would not have been possible before the web,” Amaral said in a press release. “Previously, maybe researchers would recruit undergrads on campus, and maybe get a few hundred people. Now we have all these online resources available, and now data is being shared.”

The four new personality types are based on the five basic personality traits of open-mindedness, extraversion, neuroticism, agreeableness and conscientiousness.

The “average” cluster is defined as people who are high in neuroticism and extraversion yet low in open-mindedness. Most people fall into this category, with females having a stronger and more frequent presentation than their male counterparts.

The “reserved” cluster is defined as people who are high in agreeableness and conscientiousness yet low in extraversion and neuroticism. 

The “self-centered” cluster is defined as people who are high in extraversion yet below average in openness, agreeableness and conscientiousness. The size of this population typically increases with age.

Finally, the “role model” cluster is defined as those who are low in neuroticism and high in all other traits.

“These are good people to be in charge of things. In fact, life is easier if you have more dealings with role models,” Amaral said.

The general trend also reveals that people’s personality types often change as they mature. Teenagers tend to be more self-centered, while older people tend to be more conscientious and agreeable.

The implications of this new study can be of particular interest to professionals such as hiring managers and mental health care providers who are looking to filter through potential candidates for specific traits.