In movies and TV shows, psychopaths are portrayed as cold, callous, and manipulative 'bad guys', who pose a particular challenge to law enforcement due to their high intelligence - think Hannibal or the Zodiac Killer.

But new research disagrees with this notion. Based on a meta-analysis of 187 previous studies, researchers have found that psychopaths actually have lower than average intellect, which means our favourite fictional villains probably wouldn't be nearly as calculating in the real world.

Psychopathy is a personality disorder that falls on a spectrum, meaning psychopaths are diagnosed by psychologists using a checklist of traits. That means you could have certain psychopathic traits, but without the right combination, you wouldn't be considered to be clinically psychopathic.

"Unlike most clinical disorders, which are characterised by a set of symptoms, psychopathy is commonly described as a cluster of relatively stable personality traits," explains the team, led by Brian Boutwell from St. Louis University.

"The traits most often associated with psychopathy are callousness, remorselessness, lack of empathy, grandiosity, impulsivity, deceitfulness, and manipulativeness."

This lack of moral direction has made Hollywood turn to psychopaths for their villains, making them extremely cunning in the process. One of the best examples of this is Hannibal Lecter from The Silence of the Lambs, who is a genius but also, you know, a vicious cannibal.

This notion that psychopaths are all geniuses is so prevalent, psychologists themselves call it the 'Hannibal Lecter myth', and Boutwell found it hard to reconcile these 'evil geniuses' with the facts. 

"Psychopaths are impulsive, have run-ins with the law, and often get themselves hurt," he told Jessica Hamzelou over at New Scientist. "That led me to think they're not overly intelligent."

Boutwell and his team examined 187 previously published studies that tackled psychopathy and intelligence. These studies involved not only psychopaths who were imprisoned, but also those who were successful.

When their meta-analysis was complete, the team found that psychopaths actually scored lower on intelligence tests compared to those who didn't have psychopathic traits, meaning the popular notion that psychopaths are inherently smart is likely the opposite to what happens in the real world.

We should point out that the study has yet to be peer-reviewed, so until the findings have been independently varified, we need to take them with a grain of salt.

But if they do bear out, Boutwell thinks they'll not only be useful in dispelling the public's view of psychopaths - they could help researchers to develop better treatments for psychopathy in the future.

Right now, the personality disorder is viewed as untreatable, meaning psychopaths do not respond to current psychotherapies like other conditions do.

And understanding how the disorder aligns with intellect could change the way convicted psychopaths are treated in prison, and sentenced, in the future.

"If they have low intelligence, you could say that they are likely to offend again, or you could say that if they have cognitive difficulties, a lengthier prison sentence is not going to help them," Boutwell says.

"You could make the argument in either direction."

Hopefully, more research will come out about the commonly held misconceptions we have about various forms of personality disorders. Not only to better inform the public but to also find better treatments for individuals who suffer from them.

The team's work is available on the preprint server bioRxiv.