The most profound statistic I learned from pick-up artists

Amid ample misogyny, the most profound statistic I learned from reading pick-up artist blogs is the this: In the only place we have good data (Europe), the variance in the number of heterosexual partners is more than an order of magnitude larger for men than women. I think this fact, properly internalized, makes the world look dramatically different and a bit less confusing. Let me explain the data.

For heterosexual relations, the average number of partners is mathematically required to be equal for a population with as many men as women.  (Every new sexual relationship increases both the male average and the female average by 1/2N, for a population of size N.)   However, the variance in the number sexual partners for men and women can be very different.   When a silverback gorilla has a troop of 6 breeding females (while 5 of his male compatriots are dead or banished), then the average number of partners for the men and women is equal: one.  But the female variance is zero, while the male variance is five.

To motivate their simulation study on the effect of gender differences in sexual partner variance on gender difference in sexually transmitted disease infection rates, Gouveia-Oliveira and Pedersen (PubMed abstract, full text PDF) collected all publicly available data on the width of the distribution for number of sexual partners for men and women with unbiased sampling of subjects.  It is gathered in their Table 1, reproduced below.

Country and year of study	Var(M)	Var(F)	IQR(M)	IQR(F)	ratio
Finland 1971 (Haavio-Mannila, 2001)	353.4	16.0	-	-	22.1
Britain 1992 (Johnson, 1992)	6575.0	165.3	-	-	39.8
Finland 1992 (Haavio-Mannila, 2001)	368.6	67.2	-	-	5.5
Russia 1996 (Haavio-Mannila, 2001)	309.8	31.4	-	-	9.9
Finland 1999 (Haavio-Mannila, 2001)	420.3	88.4	-	-	4.8
Sweden 1996 (Lewin, 1998)	1172.7	70.0	-	-	16.8
Britain 2000 (Johnson, 2001)	1239.0	94.1	-	-	13.2
Denmark 1992 (Meldbye, 1992)	-	-	10.1	5.9	1.7
Denmark & Sweden 2000 (Jaeger, 2000)	-	-	13.0	4.2	3.1

(Here,"Var" is variance and "IQR" is the interquartile range, i.e. the difference between the 75th and 25th percentile.)

Now, remember that the variance is the square of the standard deviation. That means that width of the curve for men is likely at least 3 times wider (and perhaps much more) than women.   The distributions are skewed because it's impossible to have a negative number of partners, which leads to a lot of celebate men, and to a small minority of the men having most of the sexual partners.

Of course, there are several qualification.  Even in the same country there are large discrepancies, and I'm not sure if they're due to different measurement techniques or what.  But they point pretty conclusively to a dramatic difference between the sexes.

This data is a modern echo of the fact (popularized by Roy Baumeister's speech and covered by a NYTimes blogger) that we have about twice as many female ancestors as male ancestors.  As Baumeister emphasizes, it's hard to imagine that this wouldn't lead to large difference in mating strategies between males and females.