Sex and intelligence

Sex and intelligence research investigates differences in the distributions of cognitive skills between men and women. This research employs experimental tests of cognitive ability, which take a variety of forms, including written tests like the SAT. Research focuses on differences in individual skills as well as overall differences in general cognitive ability, which is often called g. IQ tests, which are specially designed to measure cognitive ability, usually test a variety of skills.

The population of men and women differ on average in how well they perform on some of these skill tests, but do equally well on other tests. For example, women tend to score higher on certain tests of memory, whereas men tend to score higher on tests of spatial reasoning. While these results are relatively uncontroversial, the question of whether men and women differ on average in g is a matter of debate among experts. Most studies unambiguously find that men as a population are more varied than women in g (i.e. there are more men than women at the extremes of ability).

However, determining whether men and women differ on average has been more difficult. The primary reason for expecting that men will have higher average g than women is the male advantage in brain size. Resolving this question requires the use of sophisticated statistical techniques to extract g from the results of IQ tests. Some studies find an average male advantage in g, but most do not.

History

The scientific study of the differences in mental aptitudes between men and women dates back at least as far as the mid-nineteenth century, when the question of women's voting rights arose in a number of countries. In Victorian England, for example, the philosopher John Stuart Mill argued that there were no differences between men and women, whereas the scientist Charles Darwin (in his Descent of Man) argued that women were by their nature inferior in respect to mental ability. Many of these early attempts were based on anecdotal data. However, some scientists, such as Paul Broca (1861), attempted to derive empirical results from various forms of anthropometry, namely the comparison of brain mass. With the development of psychology at the end of the nineteenth century, and the evolving focus on intelligence testing in the early twentieth century, further attempts were made by a variety of scientists to examine the mental differences between men and women. Leta Hollingworth argues that: Women were not permitted to realize their full potential, as they were confined to the roles of child rearing and housekeeping.

The findings have provoked controversy at various times, often because political implications were perceived to be attached to them. In the nineteenth century, as noted, whether men and women had equal intelligence was seen by many as a prerequisite for the granting of suffrage; in the late-twentieth century, whether men and women had different aptitudes is often taken to reveal whether disproportionate employment or payment of men is a form of sexism or simply a reflection of innate aptitudes.

SAT scores

The SAT is a voluntary, standardised test taken by many American college applicants. It is administered by the Educational Testing Service, which keeps track of the gender of test-takers and releases SAT scores by gender. In 2001, men scored 509 out of 800 on the verbal portion while women scored 502 out of 800.

The difference, however, is more pronounced and consistent on the math segment of the SAT. In 2001, men scored 533 while women scored 498. This difference tends to appear year after year.

Allegations of SAT bias

Rosser (1989 http://sq.4mg.com/IQincome.htm#G) claimed that there were four potential areas for testing bias in the SAT:

Test content in which many more men than women are referred to or depicted and where women are depicted, they are typically shown in lower status situations
Test context in which questions are set in experiences more familiar to men
Test validity in which women's academic capabilities are under-predicted while that of men are over-predicted
Test use in which women's access to educational opportunities are diminished or restricted by an institution's reliance on test scores which under-predicts their abilities.

However, many of these hypotheses are difficult to test, and there is no direct evidence women's lower scores are due to any of these factors.

Other reports

A 2001 report by Richard J. Coley of the ETS found that females often outperformed males on various measures of verbal ability, while males tended to outperform females on measures of mathematical and spatial ability. ^*

IQ and memory

A 1994 study by H. Stumpf and Douglas N. Jackson based on medical school application test scores showed that men averaged IQs about 8.4 points higher than women, while women averaged memories about 7.5 IQ points higher than men. This study, however, may be atypical.

A 1999 study by Richard Lynn found that the IQ difference between men and women is typically about 3-4 IQ points, while women usually maintain short-term memory advantages over men of about 2 IQ points. In a 2005 study published in the British Journal of Psychology Irwing, P; Lynn, R. [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16248939&query_hl=19&itool=pubmed_docsum Sex differences in means and variability on the progressive matrices in university students: a meta-analysis., Br J Psychol. 2005 Nov 96(4):505-24. which attracted media attention in the wake of the January 2005 controversy at Harvard (below),BBC reporting Lynn & Irwing study, 2005Guardian reporting Lynn & Irwing study and Blinkhorn's reply, 2005 he and Paul Irwing analyzed existing studies to report that men have an average IQ between 3.3 and 5.0 points higher than that of women; in Nature, intelligence-test designer Steve Blinkhorn argued in reply that Lynn and Irwing's analysis was critically flawed, for example by deliberately excluding a large contrary study that made up almost 45% of the subjects in the meta-analysis.Blinkhorn, S. Intelligence: a gender bender, Nature 2005 Nov 3;438(7064):31-2.

Overall average and variance

Evidence against differences in overall average IQ scores between men and women comes from several very large and representative studies. However, these studies did find that the scores of men show greater variance than the scores of women, and that men and women have some differences in average scores on tests of particular abilities, which tend to balance out in overall IQ scores.

Deary et al. (2003) performed an analysis of an IQ test administered to almost all children in Scotland at age 11 in 1932 (>80,000). The average IQ scores by sex were 100.64 for girls and 100.48 for boys. The difference in mean IQ is not significant. However, the standard deviation was 14.1 for girls and 14.9 for boys. This difference was statistically significant. In the sample studied, 49.6% are girls and 50.4% are boys. Because of the difference in variance between the sexes however, girls are in excess by 2% in the middle IQ range of 90–115. At the extreme IQ ranges, 50–60 and 130–140, boys make up 58.6% and 57.7% of the population (a gap of 17.2% and 15.4%) respectively. That is, boys were overrepresented amongst the lowest and highest IQ groups.

Evolution over time

Hedges and Nowell (1995) performed a meta-analysis of national ability surveys that cover a 32-year period. Their primary conclusion is that male scores show greater variance (more men than women at the extremes of ability) in most abilities. The use of representative samples gives them reassurance that these differences in variance are true, and not the result of differential selection by sex. Their second finding is that average differences in most abilities are small. Exceptions include moderate to strong average advantages for men in math and science and typically male vocations, and moderate to strong average disadvantages to men in reading. They suggest the male advantage in measures of typical male vocations is not predictive, but that the other strong differences are. Thus, they claim to be concerned about the relative disadvantage of men in writing and the disadvantage to women in science and math. For example, they mention that male advantage in math and science may cause inequality in income between men and women and the underrepresentation of women in these academic fields, and likewise that men may suffer greater rates of illiteracy that will push more of them towards unemployment.

Controversy

Another study performed by the American Psychological Association in response to the book The Bell Curve, which investigates the difference in intelligence between different races, determined (as did the authors of the book) that the studies available in 1995 show no major difference between males and females in regard to IQ scores. ^*

Lawrence Summers, president of Harvard University, provoked in January 2005 an unintentionally public controversy when MIT biologist Nancy Hopkins leaked comments he made at a closed economics conference at the National Bureau of Economic Research. Original Boston Globe story reporting the remarks of Larry Summers at a January 2005 conference Transcript of Summers' remarks at NBER Conference on Diversifying the Science & Engineering Workforce Summers' initial response to controversy In analyzing the disproportionate numbers of men over women in high-end science and engineering jobs, he suggested that after the conflict between employers' demands for high time commitments and women's disproportionate role in the raising of children the next most important factor might be the above-mentioned greater variance in intelligence among men than women, and that this difference in variance might be intrinsic, adding that he "would like nothing better than to be proved wrong". The controversy generated a great deal of media attention, forced Summers to make a number of apologies, and led Harvard to commit $50 million to the recruitment and hiring of women faculty.University Will Commit $50M to Women in Science, Harvard Crimson, 2005 May 16

Other differences

Grades: Women usually receive higher grade point averages than men in educational settings. This may be a result of the subjective nature inherent in grading or of average personality differences between men and women (i.e., supposedly higher female conscientiousness).
Memory: Several studies have shown women are better at certain types of memory. ^*
General knowledge: A study by Richard Lynn showed that men have more general knowledge than women. ^*
Education: In the United States, women tend to outnumber men at colleges and universities, except at technical institutions that emphasize math and science such as MIT and Caltech, where men predominate.
Academia: Men outnumber women in tenured faculty positions in math and science. Women outnumber men in tenured faculty positions in humanities fields.
High IQ societies: In many high IQ societies men outnumber women. In Mensa the male-to-female ratio is 2:1.

Brain size

In 1861, Paul Broca examined 432 human brains and found that the brains of males had an average weight of 1325 grams, while the brains of females had an average weight of 1144 grams. A 1992 study of 6325 Army personnel found that men's brains had an average volume of 1442 cm³, while the women averaged 1332 cm³. (Ankney 1992^*). The differences are smaller but persist when adjusted for body size (Ankey, 1992).

In 2005, Haier et al. reported that compared with men, women show more white matter and fewer gray matter areas related to intelligence. They also report that the brain areas correlated with IQ differ between the sexes. They conclude that men and women apparently achieve similar IQ results with different brain regions. ^*

Reasons for differences

It is possible that sexual dimorphism may exist in regard to intellectual abilities in humans. Men may have evolved greater spatial abilities, possibly as a result of certain behaviors, such as navigating during a hunt, that they were more likely to be involved in during humans' evolutionary history. Similarly, women may have evolved to devote more mental resources to understanding and tracking relationships and reading others' emotional states in order for them to be able to better understand their social situation.

Another possibility is the effects of socialization. Girls are sometimes discouraged from studying math or science. Similarly, boys are sometimes discouraged from displaying empathy, or from spending excessive time reading for pleasure. Thus, differences in intellectual abilities between the sexes may reflect which abilities each sex is more often encouraged to develop.

The above two hypotheses are not mutually exclusive; some combination of the two may be at work.

References

External links

Pinker vs. Spelke, The Science of Gender and Science
Sex Differences in the Brain, by Doreen Kimura, Scientific American
Summerstime, and the living ain't easy: Free speech and academia, The Economist Feb 24th 2005
"Be a man: Men compete harder than women. That is why they do better at work", The Economist Jun 26th 2003
Men and Women Achieve Intelligence Differently, by Janis Kelley, NeuroPsychiatry Reviews
"Is this a clever thing to say about women's IQ?"
Various medline abstracts
Website of Doreen Kimura, contains links to more papers on subject
- "Sex, sexual orientation and sex hormones influence human cognitive function"
Sex Differences in Brain Gray and White Matter in Healthy Young Adults: Correlations with Cognitive Performance

Psychometrics | Gender

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