The mismeasure of woman summarizes the science on sexual differences:
In comparing differences between the sexes, researchers use a statistical measure called d. This indicates how far apart the averages of two groups (in this case men and women) are, taking into account the range of values that contribute to each average. The value of d for adult height is around 2. There is no arguing that in any given population men, on average, are taller than women. For behavioural and psychological phenomena, a value of d greater than 0.8 is considered large, of 0.5, moderate, and of 0.2, small. Any d less than 0.2 is a negligible difference.Equipped with this statistical tool, Janet Hyde of the University of Wisconsin-Madison decided to investigate just how different men and women are. She collected all the important meta-analyses that have been conducted on differences between the sexes. (A meta-analysis combines many studies by treating the result of each as a single piece of data for statistical purposes.) Given that most of the meta-analyses she looked at addressed questions where differences were reputed to be reliable (mathematical performance, verbal ability and aggressive behaviour, in particular) she feels her results were surprising. Of the 124 effect-sizes she calculated, 30% had a value of d close to zero and in a further 48% of cases, d was small. In other words, only 22% of reported behavioural differences between the sexes are worth raising an eyebrow over.
The largest gaps were, not surprisingly, in physical attributes such as throwing velocity (d=2.14) and throwing distance (d=1.98). These closely reflect the difference in height between men and women. Another area where she found large differences was in some areas of sexuality—for example, frequency of masturbation (d=0.96) and attitudes about sex in a casual relationship (d=0.81). However, men and women reported the same degree of sexual satisfaction.
Not surprisingly, on average men were physically more aggressive (d=0.6). But in this case other work shows the danger of jumping too rapidly to a conclusion. A study done in 1994 hints that if women think nobody is watching and judging them, and there are no physical consequences, they might be more aggressive than men.