"For 100 years there’s been a consensus among psychologists that there is no sex difference in intelligence," said J. Philippe Rushton, a psychologist at the University of Western Ontario, Canada.
Recent studies, however, have raised questions about the validity of this claim, he said. One such study showed that men have larger brains than women, a 100 gram difference after correcting for body size. Rushton found similar results in a study of gender and brain size.
To determine if there was a link between gender and intelligence, and perhaps between brain size and intelligence, Rushton and a colleague analyzed the Scholastic Aptitude Test (SAT) scores from 100,000 17- and 18-year-olds.
When Rushton and colleagues weighted each SAT question by an established general intelligence factor called the g-factor, they discovered that males surpassed females by an average of 3.6 IQ points.
The g-factor uses only the tough questions in the test. "If I tell you the last four digits of my telephone number and ask you to repeat them back to me, that’s a low g-loaded memory test," Rushton explained. "But if I then ask you to repeat them back to me in the reverse order, that suddenly requires a tremendous amount more cognitive processing. It is a very high loaded g-item.