One of the most reliable findings across studies of human sexual behavior is that heterosexual men report substantially more lifetime sexual partners on average compared to heterosexual women. In theory, the numbers reported by straight men and women should be fairly similar, right? However, we often see guys reporting partner counts that are twice as high as that of women. So why is that? How do we explain this gender difference?

A new study published in the Journal of Sex Research offers some valuable insight. Using data from a nationally representative sex study conducted in Britain, researchers performed a thorough analysis of the gender gap in partner counts (note that, in this particular survey, men reported 14 partners on average compared to 7 for women). In a nutshell, what they found was that men's greater number of reported partners could be largely explained by three factors:

(1) A small number of men appeared to be skewing the average and exaggerating the overall gender difference by reporting far higher partner counts than everyone else. Specifically, men in the 99th percentile reported an average of 110 partners (versus 50 partners for women). When researchers capped partner counts at the 99th percentile, this reduced the gender gap from 7 to 5.5.

(2) Men and women tended to use different counting strategies. Specifically, men were more likely to estimate or ballpark their number of partners, whereas women were more likely to go through and actually count them. When researchers took reporting strategy into account, this reduced the gender gap further, from 5.5 to 3.2.

(3) Men and women expressed different sexual attitudes, with women being more conservative in their views on casual sex and non-monogamy. Statistically adjusting for sexual attitudes reduced the gender gap even further to 2.6 partners.

In total, 63% of the disparity in overall number of partners reported by men and women was explained by the three factors above. These findings are important not just for helping us to better understand why the gender gap exists, but also because they have implications for getting more accurate sex survey results in the future. For example, researchers may be well served by encouraging participants to count rather than estimate the number of partners they've had.

To learn more about this research, check out the short video below in which one of the study's authors, Dr. Kirstin Mitchell, describes what they did and what they found.