Friday, September 08, 2006

Sex differences in general mental ability

Medical News:

A study published in the September 2006 issue of the journal Intelligence analyzed 145 items from the Scholastic Assessment Test (SAT) in 100,000 17- to 18-year-olds and found a male IQ advantage of 3.63 points.

It also found that the g factor--the general factor of mental ability underlay both the SAT Verbal (SAT-V) and the SAT Mathematics (SAT-M) scales with the congruence between these components greater than 0.90, and that it was the g factor that predicted student grades better than the traditionally used SAT-V and SAT-M scales.

The male and the female g factors were congruent in excess of .99, and they favored males to an equivalent of 3.63 IQ points.

The male-female differences were present at every socioeconomic level, and across several ethnic groups.

The average male advantage was found "throughout the entire distribution of scores, in every level of family income, for every level of fathers' and of mothers' education, and for each and every one of seven ethnic groups," said J. Philippe Rushton, professor of psychology at the University of Western Ontario, one of the authors of the study.

The paper's results dovetail with those from several other recently published studies showing that men--surprisingly--have a 4- to 5- IQ point advantage over women by late adolescence and early adulthood. Before that age the two sexes are equal in general intelligence.

As such, the findings overturn a 100 year consensus that men and women average the same in general mental ability.

Because girls mature faster than boys, the sex difference is masked during the school years. Since almost all the data showing an absence of sex differences were gathered on school children, this might explain why the sex difference was missed for so long.

For decades, however, psychologists have accepted that men and women differ in their test "profiles," with males averaging higher on tests of "spatial ability" and females higher on tests of "verbal ability." These differences were assumed to average out.

The authors of the study, psychologists Douglas N. Jackson and J. Philippe Rushton at the University of Western Ontario, conducted the study because two recent sets of observations had raised anew the question of sex differences in general intelligence.

The first was that the general factor of mental ability--g--was found to permeate all tests to a greater or lesser extent. Thus, a "spatial" test may be relatively high on g (mental rotation) or low (perceptual speed), a "verbal" test may be relatively high (reasoning) or low (fluency), as may a "memory" test be high (repeating a series in reverse order) or low (repeating a series in presented order).

More than any other factor, the test's g loading best determines a test's power to predict academic achievement, creativity, career potential, and job performance. Hence, the question of sex differences became formulated more precisely as: "Are there sex differences on the g factor?"

Another set of observations concerned the sex difference found in brain size and the relation between brain size and cognitive ability. Studies published in 1992 at the University of Western Ontario by zoologist C. Davison Ankney, and also by psychologist Rushton, showed men average a 100-gram advantage over women in brain weight (and volume).

A 1997 study in Denmark documented that men have 15% more neurons than women (22.8 versus 19.3 billion).

Over two-dozen Magnetic Resonance Imaging studies have confirmed a brain-size/IQ correlation of about 0.40. So, if males average a larger brain, shouldn't they also average a higher IQ score?

British psychologist Richard Lynn at the University of Ulster in Northern Ireland, and Paul Irwing at the University of Manchester found that adult men consistently average 4 to 5 IQ points higher than adult women in a series of recent large-scale studies using a number of intelligence tests in various countries. (Irwing & Lynn's most recent paper appeared in Nature on July 6, 2006.)

Other researchers too have found a male advantage in general mental ability, including Prof. Helmuth Nyborg at the University of Aarhus in Denmark, who earlier this year was disciplined by his university for talking to the media about his "politically incorrect" conclusions.

Prof. Rushton agreed that "these are unpopular conclusions." He said, "only more data can determine the true nature of sex differences in cognitive ability. However, people should not be made to feel afraid to study controversial issues."

Prof. Rushton accepted that sex differences in general mental ability could help explain the "glass ceiling" phenomenon.

But he also noted the paradox that although men may have higher IQ scores, women do increasingly well in school exams.

It will be very hard to argue that selection bias caused the sex difference in this data set, the authors wrote. "That would require the assumption that there are hypothetical respondents who, if tested, would provide a compensating female-male advantage in g that would counterbalance the findings. They would have to be found at every level of SAT performance, in every level of family income, for every level of fathers' and of mothers' education, and for every ethnic group examined."


Males have greater G: sex differences in general mental ability

The G Factor: the Science of Mental Ability

The General Intelligence Factor

Black-White-East Asian IQ differences at least 50 percent genetic, scientists conclude in major law journal


At 1:13 PM, Anonymous Anonymous said...

Now if they could just keep the wet towels off the bathroom floor...

At 6:40 PM, Anonymous Anonymous said...

But if the subjects in this study included only those writing SAT tests, the results do not represent the intelligence of the general adult population. As someone who works with children with severe language and learning problems, I consistently see a caseload that is at least 70% male(developmental learning disorders are much more prominent in males). A significant number of these boys will have lifelong learning problems & will not go on to university. Many have dropped out of school by the age of 17 & 18, and/or will not write SAT tests. On the other hand, female enrolment in university continues to increase, and so are we seeing more "average" female learners entering university whereas previously, only above-average females enrolled (cream of the crop). Also, if the weight of the brain is a significant factor, then (almost) all males would be more intelligent and THAT is clearly not true.

At 6:58 AM, Anonymous Anonymous said...

Correction to previous comment, should read "developmental learning disorders are much more PREDOMINANT in males" (ratio of learning disorders, male to female is 5:1).

Excuse the error but it's not my fault - I'm a woman.

At 10:19 AM, Anonymous Anonymous said...

BTW, the highest IQ ever recorded was by a woman. Guess she just got lucky.

At 4:09 PM, Anonymous Ahrimahn said...

BTW, the highest IQ ever recorded was by a woman. Guess she just got lucky

These studies only look at averages which explains why a woman could have the highest IQ ever recorded while the IQ of the average woman is lower than that of the average man.


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