In Christina Sommers’s American.com article, “Are There More Girl Geniuses?” she writes:
Males and females appear equally intelligent, on average. But on standardized intelligence tests, more males than females get off-the-chart test scores—in both directions. The greater variance of males on intelligence tests is one of the best-established findings in psychometric literature. More males are mentally deficient, and more are freakishly brilliant.
Sommers cites one of the most comprehensive empirical studies ever conducted to test for gender differences in the variability of intelligence—“Population Sex Differences in IQ at Age 11: The Scottish Mental Survey 1932,” published in 2003 by Intelligence, the journal of the International Society for Intelligence Research (full article here). The article focuses on the results of intelligence tests that were given to a cohort of almost 80,000 11-year-old children, an extremely large sample that is noteworthy because it represented almost every child born in Scotland in 1921.
Results of the Scottish IQ tests are displayed in the graph below and show that boys outnumbered girls both for IQ scores on the low end below 95 and IQ scores on the high end above 115. Further, the share of boys achieving low and high IQ test scores increased going out towards both ends of the distribution, so that boys represented 57.7 percent of the highest IQ scores of 140 (136 boys for every 100 girls) and 58.6 percent of the lowest IQ scores of 60 (142 boys for every 100 girls).
The authors of the study concluded that “there were no significant mean differences in cognitive test scores between boys and girls, but there was a highly significant difference in their standard deviations. Boys were overrepresented at the low and high extremes of cognitive ability.” The authors speculate that their findings might “explain such cognitive outcomes as the slight excess of men achieving first class university degrees, and the excess of males with learning difficulties.”
The statistical evidence from the Scottish IQ tests showing that male intelligence is significantly more variable than female intelligence is exactly what former Harvard President Larry Summers was referring to when he said:
It does appear that on many, many different human attributes—height, weight, propensity for criminality, overall IQ, mathematical ability, scientific ability—there is relatively clear evidence that whatever the difference in means—which can be debated—there is a difference in the standard deviation, and variability of a male and a female population.
Unfortunately for Summers, he lost his job because his remarks were widely misinterpreted as having said that men are overrepresented in math and engineering because “men and women differ in overall IQ, mathematical ability and scientific ability,” which is completely different than saying there is a difference in the variability, or standard deviation, of male and female intelligence.
And even though men are overrepresented in some high-paying math and engineering fields, they are also overrepresented in many outcomes that are particularly undesirable and often deadly: more than 93 percent of U.S. prisoners are men, 93 percent of occupational fatalities are men, and more than 90 percent of fatal motorcycle fatalities are men (data available here). Greater male variability often comes at a huge cost, and perfect statistical gender parity for all outcomes is probably something most women are perfectly happy to live without.