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From http://www.nytimes.com/2007/08/12/weekinreview/12kolata.html:
EVERYONE knows men are promiscuous by nature. It’s part of the genetic strategy that evolved to help men spread their genes far and wide. The strategy is different for a woman, who has to go through so much just to have a baby and then nurture it. She is genetically programmed to want just one man who will stick with her and help raise their children.

Surveys bear this out. In study after study and in country after country, men report more, often many more, sexual partners than women.

But there is just one problem, mathematicians say. It is logically impossible for heterosexual men to have more partners on average than heterosexual women. Those survey results cannot be correct.

Sex survey researchers say they know that Dr. Gale is correct. Men and women in a population must have roughly equal numbers of partners. So, when men report many more than women, what is going on and what is to be believed?

“I have heard this question before,” said Cheryl D. Fryar, a health statistician at the National Center for Health Statistics and a lead author of the new federal report, “Drug Use and Sexual Behaviors Reported by Adults: United States, 1999-2002,” which found that men had a median of seven partners and women four.

But when it comes to an explanation, she added, “I have no idea.”

The most likely explanation, by far, is that the numbers cannot be trusted.
I know, I know, it's such a shock that people lie about sex...still, I liked the article, and I'm glad [livejournal.com profile] missmoreland posted it. Thanks!


The Myth, the Math, the Sex

By GINA KOLATA
Published: August 12, 2007

EVERYONE knows men are promiscuous by nature. It’s part of the genetic strategy that evolved to help men spread their genes far and wide. The strategy is different for a woman, who has to go through so much just to have a baby and then nurture it. She is genetically programmed to want just one man who will stick with her and help raise their children.

Surveys bear this out. In study after study and in country after country, men report more, often many more, sexual partners than women.

One survey, recently reported by the federal government, concluded that men had a median of seven female sex partners. Women had a median of four male sex partners. Another study, by British researchers, stated that men had 12.7 heterosexual partners in their lifetimes and women had 6.5.

But there is just one problem, mathematicians say. It is logically impossible for heterosexual men to have more partners on average than heterosexual women. Those survey results cannot be correct.

It is about time for mathematicians to set the record straight, said David Gale, an emeritus professor of mathematics at the University of California, Berkeley.

“Surveys and studies to the contrary notwithstanding, the conclusion that men have substantially more sex partners than women is not and cannot be true for purely logical reasons,” Dr. Gale said.

He even provided a proof, writing in an e-mail message:

“By way of dramatization, we change the context slightly and will prove what will be called the High School Prom Theorem. We suppose that on the day after the prom, each girl is asked to give the number of boys she danced with. These numbers are then added up giving a number G. The same information is then obtained from the boys, giving a number B.

Theorem: G=B

Proof: Both G and B are equal to C, the number of couples who danced together at the prom. Q.E.D.”

Sex survey researchers say they know that Dr. Gale is correct. Men and women in a population must have roughly equal numbers of partners. So, when men report many more than women, what is going on and what is to be believed?

“I have heard this question before,” said Cheryl D. Fryar, a health statistician at the National Center for Health Statistics and a lead author of the new federal report, “Drug Use and Sexual Behaviors Reported by Adults: United States, 1999-2002,” which found that men had a median of seven partners and women four.

But when it comes to an explanation, she added, “I have no idea.”

“This is what is reported,” Ms. Fryar said. “The reason why they report it I do not know.”

Sevgi O. Aral, who is associate director for science in the division of sexually transmitted disease prevention at the Centers for Disease Control and Prevention, said there are several possible explanations and all are probably operating.

One is that men are going outside the population to find partners, to prostitutes, for example, who are not part of the survey, or are having sex when they travel to other countries.

Another, of course, is that men exaggerate the number of partners they have and women underestimate.

Dr. Aral said she cannot determine what the true number of sex partners is for men and women, but, she added, “I would say that men have more partners on average but the difference is not as big as it seems in the numbers we are looking at.”

Dr. Gale is still troubled. He said invoking women who are outside the survey population cannot begin to explain a difference of 75 percent in the number of partners, as occurred in the study saying men had seven partners and women four. Something like a prostitute effect, he said, “would be negligible.” The most likely explanation, by far, is that the numbers cannot be trusted.

Ronald Graham, a professor of mathematics and computer science at the University of California, San Diego, agreed with Dr. Gale. After all, on average, men would have to have three more partners than women, raising the question of where all those extra partners might be.

“Some might be imaginary,” Dr. Graham said. “Maybe two are in the man’s mind and one really exists.”

Dr. Gale added that he is not just being querulous when he raises the question of logical impossibility. The problem, he said, is that when such data are published, with no asterisk next to them saying they can’t be true, they just “reinforce the stereotypes of promiscuous males and chaste females.”

In fact, he added, the survey data themselves may be part of the problem. If asked, a man, believing that he should have a lot of partners, may feel compelled to exaggerate, and a woman, believing that she should have few partners, may minimize her past.

“In this way,” Dr. Gale said, “the false conclusions people draw from these surveys may have a sort of self-fulfilling prophecy.”

(no subject)

Date: 2007-08-13 11:38 pm (UTC)
redbird: closeup of me drinking tea, in a friend's kitchen (Default)
From: [personal profile] redbird
I've been noting this for years. As far as I can tell, given the way some of these study reports are phrased, along with the likelihood that many people are lying (it seems statistically likely that at least one is telling the truth), another possible explanation is a difference in the average number of same-sex partners. (A man who might not tell a researcher that he's bisexual--or who identifies as "straight" despite having partners of both sexes--might still say he'd had 7 partners, counting men as well as women.)

(no subject)

Date: 2007-08-13 11:49 pm (UTC)
From: [identity profile] noire.livejournal.com
I'd seen the disparity in reported numbers before--and always wondered how the math worked...

(no subject)

Date: 2007-08-14 02:21 am (UTC)
From: [identity profile] nhradar.livejournal.com
Yeah, we should see means. Because if there's a wide variation in the number of sexual partners women have (like, say, a lot of people with 2 and a lot of people with 30), it makes perfect sense.....

(no subject)

Date: 2007-08-13 11:50 pm (UTC)
From: [identity profile] holmes-iv.livejournal.com
Hrmph. They're using the wrong measure of central tendency, if they want everything to come out equal. But I presume somebody has looked at means as well as medians...

(no subject)

Date: 2007-08-14 12:19 am (UTC)
nathanjw: (Default)
From: [personal profile] nathanjw
I would hope so but I don't dare presume it. It would be worth doing a quick sanity check on the possibility of some distributions that have such skewed medians but matching means. The NHSLS has their raw data available, if you speak SAS and want to run some histograms.

(no subject)

Date: 2007-08-14 10:35 pm (UTC)
From: [identity profile] kissoflife.livejournal.com
Have you noted or bookmarked the location of that data, perchance? I wanna look at/play with this...

(no subject)

Date: 2007-08-15 12:26 am (UTC)
From: [identity profile] holmes-iv.livejournal.com
I do speak it (or at least, I have translation available), but I'm not sure I have time at the moment. (Considering this is supposed to be a less busy time of year, this fact frightens me somewhat.) Still, I'll try to find a few minutes to play at some point, could be very interesting.

(no subject)

Date: 2007-08-14 12:52 am (UTC)
From: [identity profile] contrariety.livejournal.com
Hah! That was exactly my thought. One sentence has "means" and then the next refers to "averages."

(no subject)

Date: 2007-08-14 03:40 am (UTC)
From: [identity profile] signsoflife.livejournal.com
I hate to be contrary, but the word "mean" isn't used in the article, though it's clear from context that they think that they're saying "mean" when they say "median".

(no subject)

Date: 2007-08-14 03:45 am (UTC)
From: (Anonymous)
*sigh*

Yes, terribly sorry; I meant to say "median" which is, in fact, the word they use.

(no subject)

Date: 2007-08-14 02:18 am (UTC)
From: (Anonymous)
Exactly my thought. An extreme example...Say you have 100 men and 100 women. 5 of the women sleep with all 100 men. The other 95 women have no sleeping activities. The median number of sleeping partners for men is 5. For women it is 0. But the mean for both is 5.

My guess is that the truth is a less extreme example of this. While most women have fewer sexual partners than most men, there exists a smaller percentage of women who sleep around, and have sex with a very large number of men. The result is that the median for men is higher, but the mean should still be exactly the same.

All this assuming of course that everyone is having only heterosexual sex.

(no subject)

Date: 2007-08-14 08:03 pm (UTC)
From: [identity profile] saladpants.livejournal.com
Strangely I wasn't logged in when I wrote this...

Anyway...Slate ran an article saying almost the exact same thing yesterday. http://www.slate.com/id/2172186/

(no subject)

Date: 2007-08-14 12:09 am (UTC)
ext_3319: Goth girl outfit (Default)
From: [identity profile] rikibeth.livejournal.com
Did they specify PIV intercourse when asking about number of partners

I would not be surprised if guys counted oral and girls didn't.

(no subject)

Date: 2007-08-14 03:15 am (UTC)
From: [identity profile] chaiya.livejournal.com
Huh. You know, I did this for along time (didn't consider oral to be "real sex"). Then I had a girlfriend, and, well, there was no piv sex between us. I'm still adjusting to the change in mindset, years later, but it's a happier-making thing, oddly enough.

'Course, this also means I literally have no idea how many sex partners I've had. Such a slut, I am! :P

(no subject)

Date: 2007-08-14 12:46 am (UTC)
From: [identity profile] awfief.livejournal.com
Have you read "More Sex is Safer Sex"? http://www.slate.com/id/2033/ is an article which helped spawn the book, and the book is http://www.amazon.com/More-Sex-Safer-Unconventional-Economics/dp/1416532218

I'm in the middle of reading the book, and it has many neat ideas in there.

(no subject)

Date: 2007-08-14 12:49 am (UTC)
From: [identity profile] r-ness.livejournal.com
I've read and liked the article, but I haven't read the book yet. Sounds like I should pick it up.

Thanks for the recommendation!

(no subject)

Date: 2007-08-14 02:24 am (UTC)
From: [identity profile] st-rev.livejournal.com
The NYT's reporter and fact-checkers don't know the difference between a mean and a median. Shocker.

(no subject)

Date: 2007-08-14 02:58 am (UTC)
skreeky: (Default)
From: [personal profile] skreeky
Yeh... that...
(deleted comment)

(no subject)

Date: 2007-08-14 06:09 am (UTC)
From: [identity profile] gravitrue.livejournal.com
I tend to think we're using the evolutionary bio/psych hammer on lots of things that aren't nails. It leads to stupid stuff like considering homosexuals to be "mistakes", and gender stereotyping like that which we are discussing; human sexuality is complicated. This whole line of inquiry (or at the very least the mass media handling of it) seems to me to be geared towards judgment and the messed up western view of sex.

That said, while point 3 is interesting, points 1 and 2 don't make sense to me. They seem to presume a family structure where it costs an individual extra resources to be a father.

There are or have been plenty of cultures where either bio dads have no direct involvement with their kids (like cultures where kids belong to the mom's clan and are raised by their uncles) or where all food and resources are shared somewhat equally.

If I live in a village with twenty fertile females and manage to inseminate a whole bunch, then the other guys are likely to be helping to raise my kids. It takes a village to raise a child, a village has a certain number of child spots available, so (under the traditional/stereotype view) my grabbing as many of the available spots as possible is a genetic win for me. And if I don't impregnate those females, someone else is likely to, so there's no survival gain to the community as a whole from members refraining.

(no subject)

Date: 2007-08-14 02:57 pm (UTC)
From: [identity profile] holmes-iv.livejournal.com

I tend to think we're using the evolutionary bio/psych hammer on lots of things that aren't nails.

ZOMG yes. Preach it!

(no subject)

Date: 2007-08-14 06:36 am (UTC)
From: [identity profile] stolen-tea.livejournal.com
Humph. The only reason they came to that conclusion is that they didn't interview the 6.2 women who've had sex with *every man in America*. On average, er, median, er, whatever. :)

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