Admit it: You've taken a personality test. Whether it's an online version or something in the back of a magazine, you've answered the questions to try to put a name on your personality type, trying to unravel what makes you "you."

But researchers at Northwestern University think they may have made major inroads in solving the personality puzzle for you. They've determined there are four personality types that everyone fits into: average, reserved, self-centered and role model.

To define those categories, the researchers studied data from four online questionnaires that attracted more than 1.5 million respondents from around the world.

"People have tried to classify personality types since Hippocrates's time, but previous scientific literature has found that to be nonsense," said co-author William Revelle, Northwestern professor of psychology, in a statement. "Now, these data show there are higher densities of certain personality types."

The researchers used an algorithm to plot the questionnaire data and found four distinct personality types, based on five character traits. The study appears in Nature Human Behaviour. Here's a look and a description of the four types. Do you see yourself?

Average

The most common personality type, average people are high in neuroticism and extraversion, but low in openness.

Reserved

Reserved people are emotionally stable but not open or neurotic. They are not particularly extraverted and are somewhat agreeable and conscientious.

Role Models

Role models are low in neuroticism and high in all the other traits. They are good leaders, dependable and open to new ideas.

Self-Centered

Self-Centered people score very high in extraversion and below average in openness, agreeableness and conscientiousness.

Defining the character traits

The researchers determined the personality types based on five widely accepted basic character traits. This is how they defined them.

Neuroticism — The tendency to frequently experience negative emotions such as anger, worry and sadness, as well as being interpersonally sensitive.

Extraversion — The tendency to be talkative, sociable and enjoy others; the tendency to have a dominant style.

Openness — The tendency to appreciate new art, ideas, values, feelings and behaviors.

Agreeableness — The tendency to agree and go along with others, rather than assert one's own opinions and choices.

Conscientiousness — The tendency to be careful, on time for appointments, to follow rules and to be hard working.

A new look at personality

woman on a laptop Because online personality tests are so popular, the researchers had data from 1.5 million people. (Photo: PH888/Shutterstock)

The researchers hope this study could change the way personality types are viewed.

"Personality types only existed in self-help literature and did not have a place in scientific journals," said lead researcher Luis Amaral, Northwestern professor of chemical and biological engineering. "Now, we think this will change because of this study."

The researchers think the finding could one day be helpful for hiring managers or mental health care providers. They are now making the information available to other researchers, so they can do independent analyses.

And they are giving credit where it's due.

"A study with a dataset this large would not have been possible before the web," Amaral said. "Previously, researchers would recruit undergrads on campus and maybe get a few hundred people. Now, we have all these online resources available, and data is being shared."

Mary Jo DiLonardo writes about everything from health to parenting — and anything that helps explain why her dog does what he does.

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