For more than three decades, John Pryor has tried to come up with an answer to the question. As one of the pioneers in the study of sexual harassment, Pryor invented a test in 1987 to measure a man’s tendency to harass. Called the “Likelihood to Sexually Harass” scale, Pryor’s test has become a cornerstone for research today on sexual harassers.

His test consists of 10 scenarios. In one scenario you must imagine that you are an executive hiring a new secretary. A female candidate explains she desperately needs the job and looks at you in a way that possibly conveys she is attracted to you. How likely are you to give her the job? Offer the job in exchange for sexual favours? Ask her to go to dinner to discuss the job?

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Over the years, Pryor – a psychologist at Illinois State University – and others have used socially engineered situations in laboratories to study how well the test predicts people’s behaviour. And over time, they’ve identified these factors as the most distinctive in harassers: a lack of empathy, a belief in traditional gender sex roles and a tendency toward dominance/authoritarianism.

They also found in studies that the environment surrounding such harassers has a huge effect, says Pryor.

“If you take men who score high on the scale and put them in situations where the system suggests they can get away with it, they will do it,” he says. “Impunity plays a large role.”

Why are people in positions of power so often doing the harassing?

In recent years, a growing body of research has shown how power warps one’s perception of others and alters people’s behaviour.

“In study after study, we’re seeing that power makes you more impulsive. It makes you less worried about social conventions and less concerned about the effect of your actions on others,” says Dacher Keltner, a psychology professor at the University of California at Berkeley.

One of Keltner’s experiments, for example, found that people who see themselves as wealthier were more likely to cut pedestrians off on a crossing. Another found that those who felt powerful were even more likely to take candy from children. Other experiments have shown that powerful people become more focused on themselves, are more likely to objectify others and more likely to overestimate how much others like them.

“It becomes a kind of solipsism. You think what’s inside your head is true about the world around you,” Keltner says. “Someone like Harvey Weinstein may think ‘I’m so horny right now, so the whole world must feel that way’.”

What makes these men think women want to see all that?

One of the most puzzling and icky details from the recent string of high-profile cases is this signature move of several powerful men: exposing themselves to women, apparently with the expectation that those women are attracted to them or will be once they see their bodies.

There is, surprisingly, a scientific explanation for this. A particularly eye-opening 2011 study found that people in leadership often pick up phantom sexual signals from subordinates that aren’t really there.

The experiment designed by Jonathan Kunstman and Jon Maner took 78 adults and paired them with a member of the opposite sex. Those pairs were assigned a Lego-building project, with one person put in charge of the other. In private interviews at the end of the project, those who were appointed leaders were much more likely to have perceived sexual interest from their subordinates, even when the subordinate said in surveys that they had no sexual interest at all.

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When researchers studied video of most pairs interacting, they found the leaders much more likely to act on that misperception, touching the subordinate’s leg or gazing at them.

“Power creates this perfect mental storm for misconduct,” says Kunstman, an experimental social psychologist at Miami University in Ohio. “This tendency to over perceive romantic interest can lead to a feeling of freedom to touch, which can then lead to misconduct.”

So what are these men really after? Sex or dominance?

“The hackneyed phrase everyone always says about sexual harassment is that it’s not really about sex, it’s about power,” says Illinois researcher Pryor. “But that’s not really true. It’s about both.”

In recent years, psychologists trying to understand the relationship between power and sex have found that, for many men who score high on the harassment scale, the two ideas are often intertwined.

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“They are two sides of the same coin and so strongly fused that it’s impossible to cleave them apart,” Pryor says. “If these men have power over someone, they find it difficult not to have those sexual ideas come to mind. And more they think about it, the more that association is reinforced.”

Why is it almost always men doing the harassing?

There’s a statistical answer for this: The way our society stands now, with all its flaws, discriminatory biases, and historical and cultural baggage, there remain many more men in leadership positions than women. (At least one woman in a position of power, however, has recently been accused of harassing a male subordinate.)

There’s also a feminist structural reading of such harassment: that harassment often serves as a vehicle to exert dominance and put women in their place.

But behavioural science has also shown there are behavioural differences between the sexes, says Louise Fitzgerald, a psychologist at University of Illinois at Urbana-Champaign.

“It’s not like women are somehow immune from dark personality traits,” she says, “but we know from gender research that men are more aggressive, more socialised to seek sex and believe they have a right to it.”

How likely is the #MeToo movement to change anything?

Fitzgerald, who has spent three decades studying the devastating effects of sexual harassment, is surprisingly pessimistic about the current movement producing momentous change.

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“I remember thinking the same thing during the Clarence Thomas hearings, that the cultural moment had come and everything would change,” she says. “But here we are 20 odd years later and people are suddenly rediscovering yet again that sexual harassment exists.”

The cases now making headlines, she notes, largely involve high-profile people in Hollywood and the media. “Will that have an effect on the woman being harassed at her job at Walmart or on the factory floor? I don’t know.”

But one thing the #MeToo movement may be changing is the stigma of sexual assault and harassment, says Pryor, the long-time harassment researcher. “The #MeToo movement shows just how common these experiences are. And that may take away the silence that often allows the harassment to be hidden.”

Another important by product of the #MeToo movement may be increased interest in sexual harassment research, say Pryor, Fitzgerald and others.

When Pryor began studying sexual harassment in the 1980s, there was little support for the work. Pryor funded many of his earliest studies himself, and had to work in his spare time to develop research like his “Likelihood to Sexually Harass” scale. In the decades since, the situation has improved but only marginally, says Pryor, now semi-retired.

“With everything we’re seeing now, that will hopefully change – maybe too late to make a difference in my career – but for others this could be a turning point,” he says.