Wharton professor found small but significant link between brain size and intelligence

Penn Marketing assistant professor  Gideon Nave recently found a slight relationship between brain size and intelligence, in what was the largest study ever conducted on the subject.

Nave worked with Philipp Koellinger, an economics professor from Vrije Universiteit Amsterdam, to examine the brain sizes and cognitive abilities of more than 13,600 people. For each subject, the researchers compared MRI measures of brain size to scores on cognitive tests and measures of educational level. The results showed that larger brain size is associated with increased fluid intelligence and greater educational attainment.

The study was published in the Psychological Science journal, with additional collaboration from Penn Psychology assistant professor Joseph Kable.

Nave found, however, that the relationship between brain size and intelligence is minimal.

"[Brain] size is only a small part of the picture, explaining about 2 percent of the variability in test performance," Nave told Penn Today. "For educational attainment the effect was even smaller: an additional ‘cup’ (100 square centimeters) of brain would increase an average person’s years of schooling by less than five months."

Koellinger added that this implies that other factors, including parenting style, education, and stress, could have a larger effect on intelligence than brain size does. 

However, Koellinger added that the study has still made an important contribution. All future studies looking at the links between brain anatomy and intelligence will need to control for brain size. 

The researchers also found that even though males have larger brains than females on average, this is not correlated with a difference in cognitive performance.

The new report stated that many earlier studies have looked at the relationship between brain size and intelligence, but some did not account for the effects that confounding variables such as height and socioeconomic status could have on intelligence. 

Nave and his research team tried to correct this problem by controlling for as many factors as possible that could impact brain size, including sex, age, height, socioeconomic status, and genetic ancestry, according to Penn Today. However, the researchers added that other factors not included in his study may still confound results. 

To further remove bias, the researchers pre-registered the study and committed to publishing it even if they did not find significant results. They also used a sample size that was 70 percent larger than the combined samples of all previous studies, allowing them to find more reliable results.