Think of all the famous psychopaths you know, both real and fictional. Chances are, for every Bonnie you’ve got about 10 Clydes. That’s because we tend to think of psychos as being criminally insane men - an image that has been continually reinforced by on-screen maniacs like Norman Bates (Psycho), Hannibal Lecter (The Silence of the Lambs), Patrick Bateman (American Psycho) et al. 

Yet if Hollywood is guilty of overly-attributing cold-bloodedness to the male gender then so too is science. From the early days of research on psychopathy in the first half of the 20th century, the trait has been approached as though it were synonymous with violent criminality, which in our society is a heavily male-dominated pastime. It’s only in recent years that our understanding of the psychopath has become more nuanced, highlighting how the label might apply to greater numbers of unexpected individuals, including women.

How Many Female Psychopaths Are There?

No one knows for sure how many people are psychopaths, largely because the term is hard to define and even harder to diagnose. In general terms, psychopaths are thought to have a diminished capacity to feel empathy or guilt, which makes them more likely to commit moral transgressions. These offenses may involve violence or deceit, but can also include more subtle misdeeds like using others for personal gain or generally acting selfishly.

Popular estimates suggest that about 1 percent of men display psychopathic traits, while the figure for women is said to be between four and 10 times lower. However, with a lack of large-scale, population-level studies to back these statistics up, they remain mere speculation.

The unreliability of these estimates has recently caught the attention of Dr Clive Boddy from Anglia Ruskin University, an expert on psychopathy in the corporate world. “My research so far doesn’t really focus on female psychopaths but I did notice that the measures I use in quantitative research kept picking up more female psychopaths than theoretically expected, so I investigated the literature and found there’s little reason to expect lower numbers of females than males,” he told IFLScience.

“In my six quantitative studies, I have consistently found more female primary psychopaths than expected.” For clarity, primary psychopaths are the kind that tend to appear in movies and are characterized by callousness, superficial charm, and manipulative tendencies. Secondary psychopaths, on the other hand, display impulsivity and an inability to make long-term plans.

Based on his own surveys of white-collar workers and their experiences with psychopathic bosses or employees, Boddy says that incidence rates of female to male psychopaths are “about 1.14:1 rather than the 5:1 or 4:1 or even 10:1 quoted in the literature. This means the incidence of female (at least primary) psychopaths could be around 1 percent – the same figure that is often quoted for male psychopathy.” If we take the 5:1 oft-quoted in the literature that means that instead of around 17 percent of psychopaths being women, it could be more like 47 percent. 

Why Have Female Psychopaths Flown Under The Radar?

“All the initial studies of psychopaths were of men in prison who were psychopathic, so there’s always been this idea that psychopaths are male criminals,” says Boddy. “And I think that psychologists and the general public haven't really got over that view of what a psychopath is yet.”

These early studies – many of which were conducted in the 1940s – continued to influence researchers for half a century, and provided much of the framework for the Levenson self-report psychopathy scale (LSRP), which was developed in 1995 as a means of diagnosing primary and secondary psychopathy. 

According to Boddy, such tools “are not necessarily suitable for identifying non-criminal or non-male psychopaths,” as they fail to capture "the confounding variables related to criminality and masculinity.” Other similar scales, such as the Psychopathy Checklist–Revised (PCL–R), have also been created, yet the suitability of these devices for analyzing female psychopathy has consistently been challenged.

For example, a study conducted in 2002 found that the PCL-R is less capable of identifying psychopathy in women than in men, possibly because of differences in anxiety and negative emotions between male and female psychopaths. Another study from 2017 concluded that psychopaths of both sexes can’t be grouped together since “females with a psychopathic personality were more frequently exposed to sexual abuse, expressed more emotional difficulties, and engaged in higher levels of relational aggression.”

Largely as a result of these male-skewed notions of psychopathy, Boddy says that men who show traits associated with the condition “are more likely to be identified as psychopaths because of gender expectations.” In contrast, people simply aren’t primed to see women in this way, so females who act psychopathically are often placed in a different category.

“Many of the characteristics of psychopathy are seen as male characteristics so when women display the same characteristics they are seen as out of place and are attributed to other personality types,” he says.

How Do Male And Female Psychopaths Differ?

“There is, as yet, no reason to believe that female psychopaths have different drivers and motivations than their male peers do,” says Boddy, whose new book, A Climate Of Fear: Stone Cold Psychopaths At Work, examines the impact of psychopaths within business organizations. “They both like to hurt people, but they do it in different ways.”

To date, there have been no significant studies looking at how psychopathy is expressed in men versus women, but based on his own research and observations, Boddy suggests that there may be some natural differences in the way the two behave. “For example, as women, on average, have lower upper body strength than males then the option of physical violence to achieve desired ends may be less available to them and they may rely instead on relational aggression, flirtation, manipulation, coercion, and seduction,” he says.

Returning to his field of psychopathy in the business world, he goes on to explain that many female psychopaths actually have to modify their behavior in ways that men don’t because of gender expectations in the workplace. For instance, there is evidence to show that “if a female psychopath behaves like a male psychopath – in other words, she's overly aggressive at work – then that works to her disadvantage because it goes against role expectations,” says Boddy. “And so to get ahead, they will have to suppress that aggressiveness and be more calculating, subtle, maneuvering, and cunning.” 

Despite these claims, it’s currently impossible to provide any solid scientific data to support a fundamental difference between male and female psychopaths. The closest we’ve got is a 2014 brain imaging study that found that the neural activity patterns of psychopathic women are largely similar but not entirely identical to those of men with the same traits.

For instance, the study revealed that when processing emotional stimuli, female psychopaths display reduced activation in the brain’s key emotional centers like the amygdala and anterior cingulate cortex, thus replicating previous findings in male psychopaths. However, unlike their male counterparts, the women in the study also showed abnormal activity in a brain region called the temporoparietal junction. 

Exactly how this translates into behavior is yet to be determined, and the full neurological correlates of psychopathy in women are still unclear. What is apparent, however, is that while male and female psychopaths share the same underlying traits, how this manifests can differ between genders.

Perhaps that’s something Hollywood can run with.