The scientific case that an increase in grows students’ abilities is not a new one. But figuring out exactly how much an additional stretch of schooling earns someone in terms of is a complicated challenge. One plausible reason more educated people tend to be more intelligent, after all, is that smarter youths are more likely to stay in school. Anyone who wants to ascertain whether an extra year of education has real cognitive benefits has to devise ways to account for that.
A new meta-analysis blends the results of 28 studies that all took measures to mitigate this problem. Based on data from more than 600,000 participants, all told, psychologists Stuart Ritchie and Elliot Tucker-Drob have arrived at a rough estimate of how much an added year of education lifted participants’ IQ scores, on average: between 1 and 5 points.
that result, however, requires some context. “This is a very sophisticated statistical analysis,” says psychologist Richard Haier, professor emeritus at the University of California, Irvine. “And yet there’s no doubt in my mind there will be a lot of misunderstanding about it.”
First, the estimates of IQ improvement depend on the type of study. In their analysis—the first to quantitatively distill the data on this question—Ritchie, a postdoctoral fellow at the University of Edinburgh, and Tucker-Drob, an associate professor at the University of Texas at Austin, examined three types of study designs, producing different estimates for each one. They included studies in which:
“They all used a cognitive test of some kind,” Ritchie says—measuring vocabulary, , verbal and nonverbal reasoning, or other abilities—and the results in each category were aggregated. (The studies focused only on education after age 6.) The three study types respectively yielded estimated IQ increases of approximately one point, two points, and five points per additional year of schooling.
The results are “not really controversial within the field,” says Haier, who is editor of the journal Intelligence. (Ritchie and Tucker-Drob also serve on its editorial board). “It really just documents something that has kind of been suspected for years.”
It’s not clear yet exactly how education might increase IQ scores, or whether effects of schooling build up with each passing year. (So don’t assume that earning a four-year degree is going to pump up your IQ score by 20 points.) Further, IQ and general intelligence are not the same thing, as Haier points out; one is an imperfect proxy for the other. “IQ points are useful metrics,” he says, “but they’re not really a measure of intelligence directly.” Any effects of education on IQ may be related to improvements in particular skills, as opposed to a broader elevation of general cognitive ability.
There is also the open question of how much a gain of one or a few IQ points—modest, given that an average IQ score is 100—matters for real-world outcomes.
“If you or I got knocked on the head and lost two IQ points, it wouldn't make a huge difference,” Ritchie says. But previous studies show a relationship between IQ and measures such as job efficiency and performance, he notes. While more research would be required to find out whether the sort of IQ gains suggested by the latest report lead to improvements on such outcomes, Ritchie says, it’s possible that “if everyone was two IQ points higher, you’d have just a little bit higher efficiency, fewer accidents.” On a societal scale, “that could end up saving quite a lot of money.”
Another potential takeaway, as psychologist (and PT blogger) Jonathan Wai has articulated, is that if a whole year’s worth of studying raises IQ by only a modest amount, shorter-term cognitive training programs—the effectiveness of which has been disputed—are unlikely to have much practical impact.
The new report does reaffirm the conclusion of psychologists that intelligence—despite being heavily influenced by —is subject to change. The public may not yet be on the same page, according to Ritchie, despite previous research reviews in tune with his paper. “I think the idea that IQ is completely set in stone is still hanging around,” he says. “I think, in this case, we have some of the strongest evidence that it’s not.”