Sexual Frequency

The big mystery is why our frequency of sex changes as much as it does. Marginal Revolution asks today why we have sex so little if we value it so much? Tyler has missed the flip-side of the argument: namely, why do we have sex so much sometimes but not other times?

Prompted by a reader, the Marginal Revolution post gives 12 (mostly serious) reasons why people don't have that much sex:

To put things short, there is an inexplicable shortage of sex.  Given that studies show that women and men enjoy it more than most other activities (on average, not on the margin I'll grant), and given its intrinsically low cost, it appears that even a crude approximation of a utility maximizing person would probably spend much more time having sex than most do.

I don't have an answer for this. What I can say is that the problem is even deeper (no pun intended).

Specifically, most people have a frequency of sex that changes a great deal over 1) their lifetime, 2) their time with the same partner, and 3) even the time of year, week, or 24 hour day (I'll leave month out for obvious reasons).

To an economist this implies that there are huge changes in the terms-of-trade between sex and other activities in which we might partake. Either our relative enjoyment of sex fluctuates a lot, or the opportunity costs of it fluctuate a lot. In economic jargon, either our (internal) marginal rate of substitution of sex for other activities changes a lot, or our (external) marginal rate of transformation for other activities changes a lot.

One point that Tyler touches on is that the cost of sex is low, and I'll add that it appears to be relatively constant. This isn't quite correct; most of the time the cost of sex is low, and occassionally it is extremely high (say, during affairs). Fortunately, I don't think this latter point it too important for most people most of the time.

Now, I can't speak for others, but my perception as a man is that the marginal utility of sex is both high and relatively constant as well. (My friends know my joke that men have a 1 to 10 scale for sexual enjoyment, where the first 9 points are awarded for a partner showing up). My guess is that the scale for women is not that extreme, but again, an interested partner is probably the most important factor.

Unfortunately, these observations make sex even more of an anomaly. For if the marginal utility and marginal cost of sex are relatively constant, then changes in our consumption of sex must be driven by changes in the marginal utility and marginal cost of other activiites.

But if this is the case, we must be substituting something for sex, and vice versa. But what is that? Watching television? I submit that there are no candidates that cover a reasonable number of possibilities.

Another factor that might explain this is fixed costs. Perhaps our frequency of sex varies with our ability to adequately cover the fixed costs. I think there is a lot to be said for this argument, but it raises another problem. Namely, it is well known in economics that fixed costs lead to agglomeration. If fixed costs are the reasons we don't have sex that often, then once we overcome those fixed costs we should have sex a lot - implying that bouts of multiple acts and by extension orgies should be common. Again this doesn't seem to be the case.

The upshot of this is that there is something very funny going on with sex that we probably can't explain very well with economics.

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Comments

[Mike]

Maybe it has something to do with the fact that sex involves two people, i.e. if I want sex every morning and my wife wants sex every night, the end result would be little sex, and much frustration.

Now, I don't think this particular example is very likely the answer to the question, but sex does follow from sort of an unusual economic relationship - each person is both an exclusive supplier and exclusive consumer for the same product, and they affect each other in subtle ways.

[Angie]

I would have no issue with having sex anytime ... any place ... the issue is finding the right person.

As it is, I find having sex with myself the only sex I'll have in the near and distant future since I'm so damn picky! lol

[Dave Tufte]

REPLY TO MIKE'S COMMENT

I think of sex like trade, and I posted as much in a second post a few hours after this one.

There may be some merit in Mike's description of a sexual partner being a monopolist (the exclusive supplier in monogamous relationships). A monopolist maximizes their benefit by reducing the quantity of "stuff" that the offer. So there is some room for denying sex as an outcome.

But, I can't see this argument going far. The reason is that each partner is both a monopolist and a monopsonist (the rarer case of a single buyer rather than a single seller). So what we would have is two monopolists colluding, and two monopsonists colluding, and frankly I'm getting lost at this point. I'm interested in pursuing this argument, but for right now I can't even see how to go forward.

[Dave Tufte]

REPLY TO ANG'S COMMENT

I'm a happily married man, so I won't touch most of this.

But I'm very curious what was going on inside my head when I went to Angie's blog a few weeks ago (Ang's Weird Ideas http://www.ang6666.blogspot.com/), poked around a bit, and decided it was an interesting and unusual blog written by an Asian man named Ang. I guess I owe her a belated Happy Mother's Day!

[Angie]

ROFL Dave! Sorry!!! Never meant to confuse!!! You have actually now made my day!!! :)

[Dave Tufte]

ROFL2. You may be the first woman ever to be pleased that she was confused with an Asian man. ;)>

[N. Beckmann]

Sex leads to having babies (hopefully married sex). Try chasing 2 small children around all day along with doing the cooking, cleaning, errands and meeting you at the train station and see how sexy you feel at the end of the day.

[Curmudgeon]

N. Beckmann has provided the definitive excuse, er, reason. Michele Catalano conspicuously excepted, there is a whole world full of horny husbands and exhausted mother wives.

[Dave Tufte]

REPLY TO N. BECKMAN:

I have two kids (2 and 6) and I agree.

But, having said that, ask anyone in a relationship if they are getting enough. The key point is that the committed relationship should make sex cheaper/easier and therefore more likely. Yet, it doesn't always work that way. Why?

[Dave Tufte]

REPLY TO CURMUDGEON:

I don't think this is definitive at all. There are lots of surveys out there that show that married couples have more sex than singles do (which isn't really surprising given the search costs that others have mentioned).

I think this is still missing the big picture. No one out there is too tired to watch TV. Sex simply isn't that hard (no pun intended). Yes it is time consuming. Yes it is inconvenient. But if these things matter so much then sex can't be that valuable to us. But that is precisely what people don't say. Marginal Revolution's original post is still right: if sex is so great, and we have ways (like marriage) to reduce its cost, then we should have a lot more of it going on.

[jmm]

individuals are complicated. sex may have been a big reason for most couples to continue, but not the only or the primary. Sex can be seen as a means to an end, whether economically, psychologically, or sociologically. Sex doesn't have simply one valence: it can be self-sustaining, or hang on any number of motivators. If we assume, as Freud did, that it's a drive, any opportunity for, or lack of, sex, provides ways to satisfy the drive, or to attend to the underlying motivation. We don't have to believe in Freud to understand that sex can be both self-motivating, or reflective of other needs or desires. Economics is an interesting side track, but not a very good general explanation of sex, especially considering biological or social comcomitants.

Recent research has suggested that males "fall in love" much more easily than females. That doesn't say anything about the number of partners, or about "LOVE", or even about long-term connections. But it may suggest why this is mostly a male conversation about something more thoughtful females mights ignore.

[Dave Tufte]

Yikes. Less syllables and better punctuation please.

I think your position is solid, and its nice to have someone chime in with a perspective from psychology.

I will grouse though that economics may be more than an interesting side-track on this issue. The proof is in the pudding, and economic techniques have been underutilized in this area. We may not end up with a better explanation, but for right now we are definitely doing poorly from lack of trying.

I'D ALSO LIKE TO POINT THE DISCUSSION BACK TO WHAT I SEE AS THE BIG QUESTION: IF SEX IS SO GREAT, WHY DON'T WE HAVE MORE OF IT (WE KNOW PIZZA IS GREAT, BUT WE HAVE A PRETTY GOOD IDEA OF WHY WE DON'T EAT IT ALL THE TIME). BUT, WHAT'S UP WITH SEX?