Before this year, one of the scientists who went on to argue for the existence of personality types didn’t believe that personality types could even exist. Yet in September, Northwestern University professor William Revelle, Ph.D. and his colleagues presented a controversial study arguing for personality types in Nature Human Behavior. They claim that personalities fall into four distinct clusters that aren’t completely separable: average, reserved, self-centered, and “role model.”

When Inverse originally reported on this finding, study co-author and postdoctoral fellow Martin Gerlach, Ph.D. told us that “in addition to our careful computational analysis, the strongest argument [for personality types] is that we can find the same types across four different datasets that use different questions and were collected by different researchers.”

These four fractions emerged out of survey responses from 1.5 million people who live around the world. These respondents answered questionnaires specifically designed to test how closely they aligned to the Big Five — widely accepted basic personality traits. These are neuroticism, extraversion, openness, agreeableness, and conscientiousness.

average personality
The traits paired with "average."

As the team analyzed this massive heap of responses, four highly-dense clusters of personalities began to appear. When they went to replicate the findings, the four clusters — here, called types — emerged again.

While unscientific personality type tests may tell you something fun, like you’re a Hufflepuff or an INFP, this personality type study is here to tell it to you straight. Case in point: Most of us fall into the “average” cluster. This group scores a bit higher in neuroticism and extroversion than in agreeableness and conscientiousness but is mostly characterized by an average score in all traits. In the video at the top of this article, co-author Luís Amaral, Ph.D. a professor of chemical and biological engineering, says “there is very little to say about average.”

Meanwhile, “role models” score low in neuroticism and high in all other traits, and reserved people aren’t very neurotic and are the most emotionally stable. The self-centered group, the authors explain, are disagreeable extraverts who are not hard-working.

Luckily for all of us, the researchers also say that personality types likely shift as people get older. You don’t have to be self-centered forever, if you pay mind to becoming more conscientious and agreeable.

As 2018 winds down, Inverse is highlighting 25 surprising things we learned about humans this year. These stories told us weird stuff about our bodies and brains, uncovered insights into our social lives, and illuminated why we’re such complicated, wonderful, and weird animals. This story was #23. Read the original story here.