Sex and Psychology - IQ

IQ

According to the 1994 report "Intelligence: Knowns and Unknowns" by the American Psychological Association, "Most standard tests of intelligence have been constructed so that there are no overall score differences between females and males." Differences have been found, however, in specific areas such as mathematics and verbal measures.

When standardized IQ tests were first developed in the early 20th century, girls typically scored higher than boys until age 14, at which time the curve for girls dropped below that for boys. As testing methodology was revised, efforts were made to equalize gender performance.

The mean IQ scores between men and women vary little.

Several meta-studies by Richard Lynn between 1999 and 2005 found mean IQ of men exceeding that of women by a range of 3-5 points. Lynn's findings were debated in a series of articles for Nature. Jackson and Rushton found males aged 17–18 years had average of 3.63 IQ points in excess of their female equivalents. A 2005 study by Helmuth Nyborg found an average advantage for males of 3.8 IQ points. One study concluded that after controlling for sociodemographic and health variables, "gender differences tended to disappear on tests for which there was a male advantage and to magnify on tests for which there was a female advantage." A study from 2007 found a 2-4 IQ point advantage for females in later life. One study investigated the differences in IQ between the sexes in relation to age, finding that girls do better at younger ages but that their performance declines relative to boys with age. Colom et al. (2002) found 3.16 higher IQ points for males but no difference on the general intelligence factor (g) and therefore explained the differences as due to non-g factors such as specific group factors and test specificity. A study conducted by James Flynn and Lilia Rossi-Case (2011) found that men and women achieved roughly equal IQ scores on Raven's Progressive Matrices after reviewing recent standardization samples in five modernized nations. Irwing (2012) found a 3 point IQ advantage for males in g from subjects aged 16–89 in the United States.

Differences in brain physiology between sexes do not necessarily relate to differences in intellect. Haier et al. found in a 2004 study that: "Men and women apparently achieve similar IQ results with different brain regions, suggesting that there is no singular underlying neuroanatomical structure to general intelligence and that different types of brain designs may manifest equivalent intellectual performance. 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 (which used in language processing) correlates with IQ.

Some studies have identified the degree of IQ variance as a difference between males and females. Males tend to show higher variance on scores, though this may differ between countries. A 2005 study by Ian Deary, Paul Irwing, Geoff Der, and Timothy Bates, focusing on the ASVAB showed a significantly higher variance in male scores. The study also found a very small (d' ≈ 0.07, less than 7%, of a standard deviation) average male advantage in g. A 2006 study by Rosalind Arden and Robert Plomin focused on children aged 2, 3, 4, 7, 9 and 10 and stated that there was greater variance "among boys at every age except age two despite the girls’ mean advantage from ages two to seven. Girls are significantly over-represented, as measured by chi-square tests, at the high tail and boys at the low tail at ages 2, 3 and 4. By age 10 the boys have a higher mean, greater variance and are over-represented in the high tail."

A psychological study was conducted where about 1200 high school graduates were recruited to take tests looking at each of their verbal, reasoning, spatial abilities, and general scholastic knowledge. Male and female performances were compared through these tests. As a result of this testing, it was discovered that males had a higher mean score on all four tests than the mean score of the females who participated in the study. In 1995, it was suggested by Charles Lewis and Warren W. Willingham that patterns of gender differences on IQ scores can change because of the selectivity of the sample itself. They argued two factors played in giving the males an advantage: the greater male variability and the sampling of a greater proportion of women.

Another study on intelligence came up with similar findings. Young adolescents were asked to volunteer in this study and completed various assessments including ones looking at language, math, and sciences skills as well as the Toulous-Pieron test of attention and the Dominoes test. While one sample of children completed these assessments, another sample completed these plus another handful. The tests results from both samples show a null sex difference in general intelligence in young adolescents. Researchers concluded that since g does not differ through academic and cognitive abilities in young adolescents, male or female, and that some other factor must be responsible for the variance between the sexes.

It was believed at one point that Gf, or fluid intelligence, can be used to be systematically detect sex differences in general intelligence if there are any. The PMA Inductive Reasoning Test, Cattell’s Culture-Fair Intelligence Test, and the Advanced Progressive Matrices were used to test a group of about 4000 high school graduates. Through the results of these tests, researchers discovered that females perform better in the PMA Inductive Reasoning Test and males perform better in the Advanced Progressive Matrices assessment. There was no sex difference noted from the results of the Culture-Fair Test. Sex difference in fluid intelligence was proven to be non-existent in this study.

While research has shown that males and females do indeed each excel in different abilities, math and science might be an exception to this. Achievement in math and the sciences gives females an advantage because it requires effective communication and the ability to comprehend abstract ideas. On the other hand, males have an advantage also, due to the fact that on average men perform better at visuospatial abilities.

While some think that IQ scores are the best way to reach conclusions about cognitive sex differences, this theory is not used consistently to measure intelligence. These tests have been complied over the years so there is no sex difference. This was done in order to keep one sex from gaining an unfair advantage over the other in performance. Although this would imply that males and females have about the same IQ scores on average and most researchers maintain this view, some researchers have concluded that men have slightly higher IQ scores than women.