When a guy tells you the number of people he’s slept with, it’s likely to be more of an estimate than an exact calculation, according to a new study. This might go some way towards explaining the disparity between the average number of sexual partners between men and women.

Researchers analysed the responses of men and women from a British sex habits survey of 15,000 people. Results found that men reported an average of 14 lifetime partners while women reported seven – and University of Glasgow researchers wanted to know why. 

“We found three main factors that explained two-thirds of the gap: a greater tendency among men to report extreme values, a greater tendency among women to count rather than estimate, and gendered difference towards casual and non-exclusive sex,” lead author Dr Kirstin Mitchell, from University of Glasgow, told HuffPost UK.

Individuals who reported very high numbers of partners skewed the average, and this effect was stronger for men than women. Men and women at the top end reported 110 and 50 or more partners respectively. Excluding these men and women reduced the overall average, closing the gender gap.

The gap reduced further when ‘accounting strategy’ was taken into consideration, where men estimate, rather than count their sexual partners. In the study, among those who said they’d slept with between five and nine people, almost a quarter (24%) of men estimated their tally compared with 15% of women.

Sexual attitudes also had an impact on reporting. Women were generally more conservative in their sexual attitudes than men. They were less likely to view one-night stands as ‘not wrong at all’ (9% versus 18%) and more likely to view a married person having an affair as ‘always wrong’ (65% versus 57%). Adjusting for these attitudes narrowed the gap even further.

Investigating a number of other explanations, they found that excluding paid-for partners made only a small difference to the gender gap, but gender differences in reported non-UK resident sexual partners had a modest impact over a five-year period.

Dr Mitchell called on people to keep a proper count of how many sexual partners they’ve had, rather than guessing.

“Accurate reporting of sexual partners is crucial for many reasons, including assessing individual risk of sexually transmitted infections (STIs) and estimating the rate of STI/HIV transmission,” she said.