Since there are roughly the same number of heterosexual men and women in the world, shouldn’t the average number of partners for both men and women be the same? A Swedish study from the 1990s–which collected information on the sexual history of 2,810 Swedes–shares a few eye-opening theories. From The Mathematics of Love.
Much like several surveys that had gone before, the scientists found that the average number of sexual partners was actually relatively low: around seven for heterosexual women and around thirteen for heterosexual men.
But before we start reinforcing any old-fashioned theories about promiscuous men and chaste women, the eagle-eyed among you might question this discrepancy. And you’d be right to do so. By virtue of the fact that there are roughly the same number of heterosexual men and women in the world and that sex has to occur between two people, the average number of partners for both men and women should be the same. And yet, the difference in male and female averages comes up time and time again in surveys of this kind.
There are a few possible explanations for this difference. Perhaps men are more likely to exaggerate (or “lie,” as it’s known in the literature). Perhaps men and women have different definitions of what has to take place to add a partner onto their total.
A slightly more persuasive argument revolves around the fact that there may be some women with an unusually high number of sexual partners who are underrepresented in the study. For example, imagine if the next woman they interviewed had slept with 3,000 people. Just this one extra data point would be enough to increase the average number of partners for all females from seven to eight, highlighting again the big issue with using the arithmetic mean to represent the average.
But perhaps more significantly, it appears that the way men and women arrive at their number is different. Women tend to count upward, listing their partners by name: “Well, there was Harry, then Zayn, then Liam . . .” This does tend to give quite accurate results, but if you forget anyone while counting, you are prone to underestimating your true number of partners. Men, on the other hand, are much more likely to approximate: “Say . . . five a year for the last four years.” Again, an acceptable method, but it does rather leave you at risk of overestimating. This theory is strengthened when you realize that a surprising number of male answers happen to be divisible by five.