But the actual number of times that men think about sex in a day is not clear-cut in scientific research. There is no perfect technology that taps into one's sexy brain waves.

　　What researchers really do is come up with clever ways of asking people what they're thinking about. They call it "experience sampling." So, in a recent study, Ohio State University researchers gave people a clicker and were asked to hit one of three buttons on it—sex, food, sleep—every time the thought of one of those things came to mind. Their study showed that the average man had 19 thoughts about sex in a day.

　　But the design of the study could have influenced the frequency count, writes cognitive scientist Tom Stafford in a new column. If you tell people to try to notice every time they think about something, you might very well increase the frequency of their thoughts about that thing. (Researchers call this the "white bear problem.")

　　男人每隔多久就会性趣盎然？

　　Other researchers—who use different sampling methods—get different results. So, a phone-based survey that asked participants more free-form questions seven times a day found that men think about sex less than they think about "food, sleep, personal hygiene, social contact, time off, and (until about 5 p.m.) coffee."

　　If you put these two studies together, as Stafford does, it's obvious that the technique influences, if not outright dominates, the phenomenon being studied.

　　And yet the experience sampling method has gotten more popular, in part because everyone has a little computer in their hands all the time, which makes surveying much, much, much easier. "Smartphones are an ideal platform for conducting Experience Sampling Method (ESM) based studies," a recent review of sampling techniques found.

　　But it's difficult to judge a person's thoughts, no matter what technology people use. The lead researcher in the Ohio State study, Terri Fisher, provided a self-critique of her study, which applies to many of them.

　　"We weren't able to study how long the thoughts lasted or the nature of the thoughts. We also don't know if all of our participants followed the instructions and really clicked every time they had the sort of thought that they were supposed to track," Fisher wrote. "However, even if they didn't, the fact that they were supposed to be clicking probably made them more aware of their thoughts about their assigned topic than they might otherwise have been, and that would have been reflected in their daily reports."

　　The perfect technology would directly measure one's brain activity and somehow translate that into the number of sexual thoughts one had, but even that might prove very difficult. What we call "a thought" is not the discrete thing that we like to pretend. "There’s also the tricky issue that thoughts have no natural unit of measurement," Stafford writes. "Thoughts aren’t like distances we can measure in centimetres, metres and kilometres. So what constitutes a thought, anyway? How big does it need to be to count? Have you had none, one or many while reading this?"

　　Perhaps the more interesting question is why we want to quantify this kind of thing at all. Does it matter if men think of sex—however defined—12 times a day, or 19, or 7, or 400?

　　These numbers reduce a whole set of arguments about the relative sexualities and norms of men and women, detaching the feelings from the lived experience of people.

　　That may be useful rhetoric for proving that men are pigs or women should be chaste or whatever, but the data says more about the limitations of our survey technologies than the nature of human sexuality.