I carried out a major five-year study and found that men have got no idea about the sex lives of women

Over the past five years, the research firm Ipsos has surveyed tens of thousands of people across up to 40 countries about our misperceptions of social realities. The results came pouring in, on everything from immigration and obesity levels to how many teenage girls give birth each year and whether murder rates are going up or down.

From all of these so-called “perils of perception” studies, one of the most unsettling findings is how skewed a picture men have about women, and particularly about women’s sex lives.

The most striking misconception across all our surveys is that British men think women aged between 18 and 29 have sex 22 times a month on average, when the reality is a much more mundane five times a month.

It’s true that everyone guesses that everyone else is having more sex than they really are. Women in Britain think men are having sex 14 times a month, when the reality is also around five times.

But the gap between perception and reality is widest when it comes to men’s views of women. Men don’t guess so incorrectly about other men, while women don’t guess as incorrectly for both men and women. This is the only part of the data that’s ridiculous. And this is not just in Britain: there is a near identical pattern in the US.

We’ve conducted some new analysis, looking at the responses in more detail and, depressingly, this overblown view of women’s sexual activity is driven mostly by younger men. The average guess among men aged 34 and under is that young women are having sex 33 times a month, compared with a guess of “just” 14 among older men.

So young men have a real issue with how they see women’s sexual activity.

There are only two explanations for this – and both are pretty grim. Both are related to what we’re told by the media and broader cultural cues, as well as how we think, and the biases and tricks our brains play on us.

Men’s massive errors are, therefore, likely to be due to a twisted mental image drawn from the representation of women in the media, entertainment, advertising and myriad other cultural cues, combined with men’s own fragile egos, thinking that women are having more sex than them.

But this is not the only area where men are very wrong about women – they also systematically underestimate how many women experience sexual harassment.

On average, across the 10 countries where we asked this question, men said that they think 41 per cent of women have experienced sexual harassment at some point during their lives, when 58 per cent of women say they actually have. Women are again much closer to the reality of their own experience, and on average guess that 51 per cent of women as a whole have experienced harassment at some point.

In every country we’ve asked this, men guess lower than women. For example, in Italy, 51 per cent of women say they’ve experienced sexual harassment, women guess it is 47 per cent, but men guess that just 34 per cent of women have been sexually harassed.

The interesting thing is that it’s only really these experiences of sex and sexual harassment where men are more wrong than women – we don’t see the same pattern of men being much further from reality on other equality measures, such as the pay gap or leadership roles.

For example, both men and women think that around one in five of the CEOs of the top 500 companies in the world are women, when it’s actually only 3 per cent. So we have a hopelessly optimistic view of the progress of women in leadership – but both men and women are equally wrong.

Similarly, both men and women think that, at the current rate of progress, pay equality will be achieved in Britain by around 2035, when it’s actually going to take until 2117, an additional 82 years. But again, there are no significant differences in misperceptions between the sexes.

Our misperceptions are a vital clue to what we really think, and there are two really important messages from how wrong we are about gender equality. First, we’re all, both men and women, too complacent about the progress that has been made towards equality, and we are not clear on how far there is to go. Second, men are particularly clueless when it comes to women's sexual behaviour, and that needs to change fast.

Bobby Duffy is professor of public policy and director of the Policy Institute at King's College London. Duffy's book, The Perils of Perception: Why We’re Wrong About Nearly Everything, is out now from Atlantic Books