In a report published Monday in the journal Nature Human Behavior, researchers at Northwestern University in Illinois identify four personality types: reserved, role models, average and self-centered…

Amaral and his colleagues named the clusters only after the clusters were located. Role models were high in every trait but neuroticism. They also appeared with increasing frequency as people aged. “These people are not mean, not rude, but kind and polite and treat people with respect,” Amaral said. The reserved type was not open and not particularly extroverted, but otherwise agreeable and conscientious.

People who scored very high in extroversion but were below average in agreeableness, conscientiousness and openness were “self-centered.” Amaral put it in a “nontechnical way”: Some people are “jerks.” Teenage males were more likely than average to be self-centered, but this proportion decreased with age.