Pretty much everyone can recall a time when they’ve been selfish or behaved arrogantly. But these behaviors are much more extreme in people diagnosed with narcissistic personality disorder (NPD). According to criteria listed in The Diagnostic and Statistical Manual of Mental Disorders (DSM), the authoritative guide to diagnosing mental disorders used by healthcare professionals, narcissistic personality disorder is a psychological disorder in which a person has an inflated sense of their own self-importance with a desperate need for attention. They also lack empathy for others. It’s not a pretty picture, but a new study adds another element to the narcissist’s profile — aggression.

Ohio State University researchers made this connection after analyzing over 430 studies on narcissism from around the globe that involved more than 123,000 participants. The findings showed that the connection between narcissism and aggression is universal. It exists despite gender, age, place of residence or whether the individual has high or low self-esteem.

The connection between narcissism and aggression is universal. It exists despite gender, age, place of residence or whether the individual has high or low self-esteem.

There were slight differences: people with higher levels of narcissism are more likely to be described as “cold, deliberate and proactive in their forms of aggression” and they become even more aggressive when they feel threatened.

“It’s a pretty straight forward message: Narcissism is a significant risk factor for aggressive and violent behavior across the board,” the study’s co-author, Brad Bushman, a professor of communication at Ohio State University, said in a statement.

“The link we found between narcissism and aggression was significant — it was not trivial in size,” explained Sophie Kjaervik, the lead author and an Ohio University graduate student, adding, “The findings have real-world implications.”

One reason for the importance of the findings is that there are plenty of narcissists out there. The National Institutes of Health (NIH) estimates up to five percent of the U.S. population fits the NPD profile. And the number is growing, especially in Western societies which tend to emphasize winning and individualism.

The research is particularly timely for another reason. Not only did it link aggression to in-person behaviors such as angry outbursts at social or business gatherings, but also included online bullying.

Dealing with a narcissist is difficult, and in extreme cases could be dangerous. If you have to do it, you may need help. Counseling by a professional is one option. Another is to join a narcissist abuse support group. There are meetups online and in- person all over the country. Some may be led therapists, others by survivors. Most are free, though some may charge a fee to cover costs of having the group meet.

The study is published in Psychological Bulletin.