Sex differences in intelligence
Sex differences in human intelligence have long been a topic of debate among researchers and scholars. It is now recognized that there are no significant sex differences in average IQ, though average performance in certain cognitive tasks varies somewhat between sexes.
While some test batteries show slightly greater intelligence in males, others show slightly greater intelligence in females. In particular, studies have shown female subjects performing better on tasks related to verbal ability, and males performing better on tasks related to rotation of objects in space, often categorized as spatial ability.
Some research indicates that male advantages on some cognitive tests are minimized when controlling for socioeconomic factors. It has also been hypothesized that there is slightly higher variability in male scores in certain areas compared to female scores, leading to males' being over-represented at the top and bottom extremes of the distribution, though the evidence for this hypothesis is inconclusive.
IQ research
Background
There is no statistically significant difference between the average IQ scores of men and women. Average differences have been reported, however, on some tests of mathematics and verbal ability in certain contexts. Some studies have suggested that there may be more variability in cognitive ability among males than among females, but others have contradicted this, or presented evidence that differential variability is culturally rather than biologically determined. According to psychologist Diane Halpern, "there are both differences and similarities in the cognitive abilities of women and men, but there is no data-based rationale to support the idea that either is the smarter or superior sex."Findings
Although most tests show no sex difference, there are some that do. For example, it has been found that female subjects tend to perform better on tests of verbal abilities and processing speed while males tend to perform better on tests of visual-spatial ability and crystallized intelligence. For verbal fluency, females have been specifically found to perform slightly better, on average, in vocabulary and reading comprehension and significantly higher in speech production and essay writing. Males have been specifically found to perform better, on average, in spatial visualization, spatial perception, and mental rotation. None of these findings, however, suggest an advantage for either sex in general intelligence, nor in fluid intelligence.Most studies find either a very small difference or no sex difference with regard to general intelligence. In 2000, researchers Roberto Colom and Francisco J. Abad conducted a large study of 10,475 adults on five IQ tests taken from the Primary Mental Abilities and found negligible or no significant sex differences. The tests conducted were on vocabulary, spatial rotation, verbal fluency and inductive reasoning.
The literature on sex differences in intelligence has produced inconsistent results due to the type of testing used, and this has resulted in debate among researchers. Garcia argues that there might be a small insignificant sex difference in intelligence in general but this may not necessarily reflect a sex difference in general intelligence or g factor. Although most researchers distinguish between g and IQ, those that argued for greater male intelligence asserted that IQ and g are synonymous and so the real division comes from defining IQ in relation to g factor. In 2008, Lynn and Irwing proposed that since working memory ability correlates highest with g factor, researchers would have no choice but to accept greater male intelligence if differences on working memory tasks are found. As a result, a neuroimaging study published by Schmidt conducted an investigation into this proposal by measuring sex differences on an n-back working memory task. The results found no sex difference in working memory capacity, thus contradicting the position put forward by Lynn and Irwing and more in line with those arguing for no sex differences in intelligence.
A 2012 review by researchers Richard E. Nisbett, Joshua Aronson, Clancy Blair, William Dickens, James Flynn, Diane F. Halpern and Eric Turkheimer discussed Arthur Jensen's 1998 studies on sex differences in intelligence. Jensen's tests were significantly g-loaded but were not set up to get rid of any sex differences. They summarized his conclusions finding "No evidence was found for sex differences in the mean level of g or in the variability of g. Males, on average, excel on some factors; females on others." Jensen's conclusion that no overall sex differences existed for g has been reinforced by researchers who analyzed this issue with a battery of 42 mental ability tests among adults and found no sex difference.
A large analysis by five researchers with a representative sample size of over 15,000 participants found no support for sex differences in IQ, neither among children nor among adults.
A 2022 meta-analysis found that even small sex-based differences in general intelligence among school-aged children were an artifact of older tests, with current test batteries showing no statistically significant difference between the sexes, but that differences in intelligence sub-types such as processing speed and visual-spatial reasoning remained even when controlling for test age. They concluded that their analysis confirmed previous findings where "no evidence was found for gender differences in the mean level of g or in the variability of g."
Variability
Some studies have identified the degree of IQ variance as a difference between males and females. Some researchers have argued that males tend to show greater variability on many traits, a view which is termed the variability hypothesis; for example, having both highest and lowest scores on tests of cognitive abilities. Other research has been published which contradicts this hypothesis, however, showing either equal variability between the sexes in some cultural contexts or else greater representation of females at the upper extreme of some measures of cognitive ability.Feingold and Hedges and Nowell reported that, despite average sex differences being small and relatively stable over time, test score variances of males were generally larger than those of females. Feingold "found that males were more variable than females on tests of quantitative reasoning, spatial visualisation, spelling, and general knowledge.... Hedges and Nowell go one step further and demonstrate that, with the exception of performance on tests of reading comprehension, perceptual speed, and associative memory, more males than females were observed among high-scoring individuals."
In regards to variability in mathematics performance, a meta-analysis by Lindberg et al. found male-to-female variance ratios ranged from 0.88 to 1.34 across studies with an average of 1.07, indicating nearly equivalent male and female variances. The authors note that greater male variability is not ubiquitous, and ratios less than 1.0 have been reported in some national and international data sets. A review by Hyde et al. also evaluated the topic of greater male variability in mathematics performance. The review found that the gender gap among the highest performers has narrowed over time in the U.S., is not found among some ethnic groups and in some nations, and correlates with several measures of gender inequality. The authors conclude that greater male variability in math performance is largely an artifact of cultural factors as opposed to innate biological sex differences.
Brain and intelligence
Differences in brain physiology between sexes do not necessarily relate to differences in intellect. Although men have larger brains, men and women have equal IQs. For men, the gray matter volume in the frontal and parietal lobes correlates with IQ; for women, the gray matter volume in the frontal lobe and Broca's area correlates with IQ. Women have greater cortical thickness, cortical complexity and cortical surface area which compensates for smaller brain size. Meta-analysis and studies have found that brain size explains 6–12% of variance among individual intelligence and cortical thickness explains 5%.Although a meta-analysis of 148 samples from over 8000 participants reported a weak correlation between brain size and IQ, men and women did not differ in IQ, and the researchers concluded that "it is not warranted to interpret brain size as an isomorphic proxy of human intelligence differences." Brain volume contributes little to IQ test performance. Outside of comparing intelligence levels of the sexes, brain size is only one of numerous factors that influence intelligence, alongside white matter integrity, overall developmental stability, parieto-frontal neuronal networks, neuronal efficiency, and cortical gyrification. Brain structural integrity seems to be more important as a biological basis.
In 2021, Lise Eliot et al found no difference in overall male/female abilities in verbal, spatial or emotion processing.
Mathematics performance
Across countries, males have performed better on mathematics tests than females, but there is the possibility male-female difference in math scores is related to gender inequality in social roles. Some psychologists believe that many historical and current sex differences in mathematics performance may be related to boys' higher likelihood of receiving math encouragement than girls. Parents were, and sometimes still are, more likely to consider a son's mathematical achievement as being a natural skill while a daughter's mathematical achievement is more likely to be seen as something she studied hard for. This difference in attitude may discourage girls and women from further involvement in mathematics-related subjects and careers.In a 2008 study paid for by the National Science Foundation in the United States, researchers found that girls perform as well as boys on standardized math tests. They attributed this to girls now taking as many advanced math courses as boys, unlike in the past.
There is also evidence that boys are over-represented among the very best and very worst performers on measures of mathematical ability and standardized measures of IQ. Some research suggests that differences in mathematics course performance measures favor females. A small performance difference in mathematics on the SAT persists in favor of males, though the gap has shrunk from 40 points in 1975 to 18 points in 2020. The international PISA exam provides representative samples. On the 2018 math PISA, there was no statistically significant difference between the performances of girls and boys in 39.5% of the 76 countries that participated. Meanwhile, boys outperformed girls in 32 countries, while girls outperformed boys in 14. On average, boys performed 5 points higher than girls. However, overall, the gender gap in math and science for boys and girls from similar socio-economic backgrounds was not significant.
On the math portion of the 2019 TIMMS, taken at a similar age as the PISA, girls outperformed boys by 3 points on average, although the difference was not statistically significant. A meta-analysis of nearly half a million participants using data from both the TIMMS and the PISA found that differences were negligible, although girls outperformed boys in some countries and the opposite occurred in others.
A 2008 meta-analysis published in Science using data from over 7 million students found no statistically significant differences between the mathematical capabilities of males and females. A 2011 meta-analysis with 242 studies from 1990 to 2007 involving 1,286,350 people found no overall sex difference of performance in mathematics. The meta-analysis also found that although there were no overall differences, a small sex difference that favored males in complex problem solving was still present in high school. However, the authors note that boys continue to take more physics courses than girls, which train complex solving abilities and may provide stronger training than pure mathematics.
The mathematics GCSE examination results in England have often been inconsistent about which sex performed better. In 2008, 14.7% of females scored an A or above, while only 13.9% of males did the same. But in 2024, only 15.5% of females scored an A or above, while 18% of males did. A 2020 analysis of gender differences in the mathematical abilities of 13 million students in Italy found that males performed better at mathematics and that this difference appeared to increase the richer the Italian regions were, which is also characterized by greater gender equality.
One line of inquiry has focused on the role that stereotype threat might play in mathematics performance differences between male and female test-takers. Systematic reviews and meta-analyses suggest that stereotype threat is implicated in performance differences on some mathematics tests, though the effect appears to vary considerably in different social contexts and for different test conditions.