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Ever since the late 1940s when Alfred Kinsey conducted the first scientific survey of American , three odd findings have been confirmed over and over again. Compared with women, men consistently report more sex partners; they report having more sex with those partners; and they report more oral sex received and provided.

How could this be? Every time a man has heterosexual sex, a woman does, too, and so each ’s number of partners, and amount and type of sex, should be roughly equal. But they’re not — not by a long shot.

The Numbers Don’t Add Up

The University of Alberta in Canada reviewed the substantial literature on men’s and women’s lifetime number of sex partners. Men on average said they have 12, but women said 4. So on average, men reported three times as many partners as women.

For example, Indiana University and University of Chicago researchers asked a representative sample of more than 6,000 adults about sex during the previous six months:

Those saying “I had partner sex"

Age Men Women

25-44 92% 90%

55-64 85% 62%

65-74 56% 38%

65-85 39% 23%

In every age group, men reported more partner sex.

In another study, the Indiana group asked a representative sample of 5,865 American men and women about oral sex during the past year.

Men Saying Fellatio Received Women Saying Fellatio Provided

18-39 68% 62%

40-49 62% 57%

50-59 49% 44%

60-69 38% 34%

70+ 19% 24%

Except for those the age 70+ group, men in every other age group say they received more fellatio than woman say they provided.

Women Saying Cunnilingus Received Men Saying Cunnilingus Provided

18-39 65% 67%

40-49 52% 53%

50-59 34% 36%

60-69 25% 23%

70+ 8% 7%

Again, in most age groups, men report providing a bit more cunnilingus than women say they received.

Number of Partners: Women Enumerate, Men Estimate

Men report more lifetime sex partners in part because the genders differ in how they come up with their estimates.

The University of Alberta researchers asked 1,787 college students to estimate their lifetime number of sex partners and how they came up with their number. Compared with men, women were considerably more likely to enumerate — that is, to count up their partners name by name. Some women said they kept running tallies — for example: "I keep a diary, and I know my current boyfriend is #6" — but most recalled their partners from .

Enumeration is notorious for producing low estimates, because memory plays tricks. People tend not to recall lovers with whom they disliked sex, or with whom they had forgettable one-night stands, or sex under the influence of drugs or .

Meanwhile, the men were considerably more likely to base their estimates on rough approximations. Their comments expressed substantially more uncertainty than the women. Many said they “just guessed.” Some came up with formulas: “Two to three a year for six years.” Many men may feel social pressure to have sex with many women, so it's not surprising that their estimates would overstate their number of partners.

Encounters That Don’t Get Counted

Another reason men report more sex than women is that on average, women live longer than men. As later life unfolds, women increasingly outnumber men. As a result, surviving older men have an easier time finding partners. Meanwhile, increasing numbers of women don't have lovers, which reduces overall sex among older women.

In addition, on average, men pursue sex more avidly than women. Men like to think of themselves as studs, so at every age, they tend to overestimate the number of women they bed. Meanwhile, most women view too-frequent sex (whatever that may mean for them) as "slutty," a label they’d rather avoid, so they tend to underestimate how often they’re sexual.

Finally, many men patronize sex workers. The research is limited, but every year, an estimated 16 percent of male Americans — some 20 million men, both single and partnered — pay for sex. Meanwhile, researchers estimate that women who work in what’s often called “the oldest profession” are only a fraction of a percent of the adult female population, perhaps around 1 million. Sex workers are an elusive group, difficult to survey or interview. As a result, their large numbers of sexual encounters probably don’t get counted, which reduces women’s overall amount of sex. Men’s visits to sex workers may also help explain why men say they receive more fellatio and provide more cunnilingus than women say they provide and receive.

Did I miss anything? Are there other explanations why the genders differ on reported amounts of sex?

References

Brown, N.R. and R.C. Sinclair. “Estimating Number of Lifetime Sex Partners: Men and Women Do It Differently,” Journal of Sex Research (1999) 36:292.

Laumann, EO et al. The Social Organization of Sexuality: Sexual Practices in the United States (1994) Chicago University Press, page 82.

Lindau, ST and N Gavrilova. “Sex, Health, and Years of Sexually Active Life Gained Due to Good Health: Evidence from Two U.S. Populations-Based Cross-Sectional Surveys of Ageing,” BMJ (2010) 340:c810.

Herbenick, D. et al. “Sexual Behavior in the United States: Results from a National Probability Sample of Men and Women Ages 14-94,” Journal of Sexual Medicine (2010) 7(Suppl 5):255.

Westerhoff, N. “Why Do Men Buy Sex?” Scientific American Oct. 2012. http://www.scientificamerican.com/article/why-do-men-buy-sex-2012-10-23/

“How Many Prostitutes Are Three In the United States and the Rest of the World?” http://prostitution.procon.org/view.answers.php?questionID=000095

“Prostitution in the United States.” https://www.hg.org/article.asp?id=30997