Studies in IQ

1 Reply

Garret Jones tweeted out this 2012 review of the research.

It is dense but interesting.

Also: discussions of IQ can be fraught with misunderstanding and improper conclusions. Too many people in our society also fetishize high IQs. I would not do that if I were you. It is not the measure of human worth.

But the science is important to understand, especially if you work in education.

Anyway, direct quotations from the report below (headings are my own):

In the Unites States, children living in poverty demonstrate less IQ heritability than their higher income peers. 

From the report: “One interpretation of the finding that heritability of IQ is very low for lower SES individuals is that children in poverty do not get to develop their full genetic potential. If true, there is room for interventions with that group to have large effects on IQ. That this interpretation of the finding is correct is indicated by an actual intervention study…”

Adoption studies show gains in children who change social environments at a young age

From the report: “We can be confident that the environmental differences that are associated with social class have a large effect on IQ. We know this because adopted children typically score 12 points or more higher than comparison children (e.g., sib- lings left with birth parents or children adopted by lower SES parents), and adoption typically moves children from lower to higher SES homes.”

Schooling matters

From the report: “It was known at the time of the Neisser et al. (1996) article that school has a great impact on IQ (Ceci, 1991). Natural experiments in which children are deprived of school for an extended period of time show deficits in IQ of as much as 2 SD…  took advantage of the natural experiment created in Norway when an extra two years of schooling beyond the seventh grade began to be required. Effects on IQ were substantial at age 19—equal to one third the size of the Flynn effect (the marked secular gain seen in developed countries, which we discuss in detail later) in Norway at the time.”

High-quality pre-k can work

From the report: “Whether or not high-quality intervention programs have sustained IQ effects, the effects on academic achieve- ment and life outcomes can be very substantial.”

Teaching matters

From the report: “Students who had more experienced teachers had higher earnings as adults, as did students for whom the quality of teaching as measured by test scores was higher. Academic gains due to having more experienced, superior teachers faded in later grades, but noncognitive gains persisted, much as for the pre-elementary intervention just discussed.”

Modernization leads to gains in IQ

From the report: “Flynn’s (1987) research showing that 14 nations had made huge IQ gains from one generation to another was known to Neisser et al. (1996). Data on IQ trends now exist for 30 nations. Gains differ as a function of the degree of moder- nity that characterizes different nations.”

Differences between the sexes

From the report: “Jensen’s conclusion that no overall sex differences exist for intelligence has been bolstered by researchers who assessed intelligence with a battery of 42 mental ability tests (Johnson & Bouchard, 2007). They found that most of the tests showed little or no sex differences. There were, however, several tests that showed a difference between males and females of 0.5 SD or more. These differences included an advantage for females for verbal abilities such as fluency and memory abilities and an advantage for males on visuospatial abili- ties such as object rotation.”

From the report: “Although we recognize the importance of evolutionary pressures in shaping modern humans, modern mathematics and writing had no counterpart in early human societies, and the changing nature of sex differences in many intellectual tasks over the last century cannot necessarily be explained with direct appeals to our evolutionary past. Because of the complexity of influences on intellectual development, we endorse a biopsychosocial model that recognizes the mutual influences of biological and psycho- social effects.”

Differences between races

From the report: “The direct evidence indicates that the difference between the races is entirely due to environmental factors and that the indirect evidence has little value.”

Expectations and stereotypes matter

From the report: “Our understanding of group differences in intellectual ability is furthered by the very large literature on psychological reactions to negative stereotypes. Steele and Aronson (1995) argued that when test takers are aware of wide- spread stereotypes that impugn a group’s intelligence (e.g., “Black people are stupid,” “Girls can’t do math”), they frequently experience the threat of devaluation—by the self, by others, or by both. The resulting arousal and anxiety can impair executive functioning on complex tasks such as standardized aptitude tests.”