Via Marginal Revolution: Consistent with many earlier studies (JSTOR), what this study found was that the ratio of male to female variance in ability was positive and significant, in other words we can expect that there will be more math geniuses and more dullards, among males than among females.
Quoting from the study:
Greater male variance is indicated by VR [Variance Ratio]> 1.0. All VRs, by state and grade, are >1.0 [range 1.11 to 1.21].
If a particular specialty required mathematical skills at the 99th percentile, and the gender ratio is 2.0, we would expect 67% men in the occupation and 33% women. Yet today, for example, Ph.D. programs in engineering average only about 15% women.
Larry Summers in his infamous talk, was explicit about this point:
…if one is talking about physicists at a top twenty-five research university, one is not talking about people who are two standard deviations above the mean…But it’s talking about people who are three and a half, four standard deviations above the mean in the one in 5,000, one in 10,000 class.
The expected gender ratio at 4 standard deviations from the mean you find a ratio of more than 3:1