The New York Times as the question, "How is it possible for sexual surveys to report that men have more sex partners than woman?" To illustrate the conundrum, they turn to mathematician David Gale who uses the metaphor of a high school prom:
“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.
Proof: Both G and B are equal to C, the number of couples who danced together at the prom. Q.E.D.”
Dr. Gale then strays into the realm of Psychology to explain the anomaly in sex survey results:
"...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.”
There can be other explanations too. Where I live in Long Beach one can drive down PCH and count at least fifty prostitutes working the stroll. If we conservatively estimate a minimum of 100 working prostitutes at any given time in Long Beach (factoring in those found in the phone book under escorts, on the internet, and found working the streets in other parts of town). If we figure 300 working days a year, and four tricks per day, we get a number that comes close to the population of sexually active males in the city, about 120,000, all from a sample of 100 women who most likely don't have a telephone, and thus don't participate in the surveys.
Granted, there can be problems too with how survey questions are asked. Interestingly, men are more likely to count oral sex as sex than women. Porn videos aside, real life three-ways are more likely to include two men and one woman than the reverse. Then there's the issue of transgenders. If a man has sex with a person in a dress with large breasts, he's likely to call it an encounter with a woman, regardless of the X or Y chromosomes.
And lastly, there's the issue of homosexuality. Laud Humphries groundbreaking work on public sex in the mid-seventies found that the majority of men he observed engaging in homosexual acts in public would state that they were heterosexual when interviewed months later in what was presented as a general health survey. I have a friend that I fooled around with in grade school. When I Goggled his name, I found that he's now a member of a conservative christian church and is married with five kids. I suspect that he would claim to be exclusively heterosexual if interviewed today, though I might be claimed in the category of lifetime sexual partners.
I remember a story told to me by a colleague when we were developing a questionnaire for a study I was working on:
Two seminarians where out having a cigarette and chatting, when they wondered if it would be OK to pray and smoke at the same time. They each decided to ask their teachers and report back to each other.
The next week, one seminarian reported that it was OK, and the other said it wasn't. The first seminarian then asked, "What did you say?"
"I asked him if it was OK to light up a cigarette while I was praying, and he said no. What did you ask?"
"I asked my teacher if while I was smoking I got the urge to pray, would it be OK to do so, and he said yes."