Posted by: Amelia | June 23, 2007

Sex & the CDC

The Center for Disease Control and Prevention release a report (PDF) that essentially displays America’s collective purity score. Bloggers and news sources are having lots of fun pulling out the juiciest numbers: only 4% of adults over the age 20 are virgins, over 20% of adults have tried cocaine or other street drugs (not including marijuana) in their lifetime, Mexican Americans have the highest rate of lifetime abstinence, etc. The two numbers that are generating the most buzz, though, are the divergent medians for number of lifetime sexual partners for men and women. From ABC News‘s summary:

A new nationwide survey, using high-tech methods to solicit candid answers on sexual activity and illegal drug use, finds that 29 percent of American men report having 15 or more female sexual partners in a lifetime, while only 9 percent of women report having sex with 15 or more men.

The median number of lifetime female sexual partners for men was seven; the median number of male partners for women was four.

So the big question is: where do men’s extra partners come from? Click “read more” to go below the jump: this could take a while.

It’s really worth reading the study itself before trying to come up with explanations. For one, the study only asked men about female partners, and women about male partners; allegations of promiscuous gay men and monogamous lesbians skewing the survey will have to go back on the shelf. Secondly, the study duly notes that “limitations of self-reported data include recall problems and intentional misreporting of behaviors.” It sounds as though the CDC did at least take some steps to reduce the hazards of self-reporting. As one blog reports:

The questionnaire, which defined sex as oral, anal or vaginal, was administered in a confidential environment designed to elicit honest answers, [Co-Author Kathryn] Porter said today in a telephone interview. Survey respondents entered a van, listened to the questions through head phones, and typed their answers into a computer without researchers being present.

Given these facts, I have come up with a few explanations for the discrepancy between men’s and women’s lifetime partners.

1) Misreporting rooted in cultural norms. Even though the CDC took pains to reduce the hazards of self-reporting, it is extremely difficult to get accurate results about touchy subjects like sex and drugs. Men may be more likely to overreport their sexual partners (and women to underreport) based on their desire to conform to cultural standards about acceptable levels of male and female sexuality. As one blogger says, “If there’s one thing my life has taught me, it is that people will lie to themselves about their sex life or lack of it just as blithely and frequently as they lie to others.”

2) Misreporting rooted in confusion. The survey implied that sexual partners include those with whom a respondent had engaged in oral sex. This is not really the standard ‘purity test’ definition of a person’s capital-N Number, particularly for younger people (and I think particularly for women). Perhaps in tandem with explanation #1, women used this confusion to fudge their numbers down, while men may have had the opposite reaction.

3) Paging Samantha Jones. It’s important to remember that the disparity is in the median number of lifetime sexual partners. We are not given a mean. So it is possible that there are a few extremely promiscuous women out there bumping up the numbers for their many male partners while not having much effect on the median for women. In other words, if those 29% of men with over 15 partners are averaging near 15, but the 9% of women with over 15 partners are averaging much higher, you could see a discrepancy in the overall median. I suppose prostitution would be a factor in a similar manner (but the comparison should not be construed as a moral judgment for either group).

4) Foreigners. The study only surveys Americans. If American men are sleeping with foreign women at a higher rate than American women are sleeping with foreign men, it would skew the results. Unlikely, but maybe.

I think misreporting probably explains most of the discrepancy, with maybe a small effect from explanation #3. I’d be really curious to hear other ideas, though.



  1. This type of statistic is consistent with many past surveys. Although there’s always bias, some of the studies are quite good. Samantha Jones seems to be the answer. You see the same phenomenon with average age at first sexual experience which is highly skewed between men and women. Do we think all teenage boys sleep with older girls, or that the average 13 year old female non-virgin is less tentative than the 13 year old female virgin?

  2. “It’s important to remember that the disparity is in the median number of lifetime sexual partners. We are not given a mean”

    Which is a shame – the mean would be a really good way of establishing bias.
    Clearly the means should be equal (for every man sleeping with a woman, there is a woman sleeping with a man – and the populations are roughly equal), so giving us that data would give us a much better picture of how much to adjust the numbers to get an accurate picture.

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