Why school is so important, distilled: Each year of schooling increases IQ by 1-5 points, and these effects persist for a lifetime. This meta-analysis concludes "Education appears to be the most consistent, robust and durable method yet to be identified for raising intelligence." pic.twitter.com/vH4wI6VIyo— Ethan Mollick (@emollick) August 18, 2020
I wrote a tweet about why I was skeptical about these claims, but before sending, I decided to actually read the paper (H/T @hillelogram). I discovered that it seems to be a well-done study that does not conclude that “each year of schooling increases IQ.” Here’s what I found.
The reason I was skeptical because the vast majority of people in the US have between 12 and 18 years of schooling. If each year of schooling increased IQ between 1 and 5 points, it would be very hard to find that signal.
The problem is that the within-group variation would be so large. Somebody with just a HS education would have between 12 and 60 points of benefit, while somebody with a graduate degree would have between 18 and 90 points.
It is possible to find these differences between groups even if groups have such high within-group variation, but it’s hard. So I was skeptical. (Also, obviously, it’s insane to think that any schooling could have 60 points of IQ benefit.)
But before hitting send I had my second thoughts and found the paper (which wasn’t linked in the original tweet, but it’s here). The first thing I found was that the paper goes to great pains to control for the problems plaguing social science statistical studies.
If you’re not up on these problems (p-hacking, file-drawer effect, the garden of forking paths), you could do worse than to read https://statmodeling.stat.columbia.edu/, or just about anything by Andrew Gelman.
I’m not an expert in these topics by any means, but they are at least aware of these problems and seem to take reasonable measures to counteract them.
OK, so what does the paper conclude? It’s right there in the abstract: “we found consistent evidence for beneficial effects of education on cognitive abilities of approximately 1 to 5 IQ points for an additional year of education.”
But, wait, you say, “Isn’t that what the quoted tweet said?” No. And it illuminates how these games of telephone distort good research. The paper is looking at the impact of the marginal impact of a single additional year of education.
That means you look at people who are going to get 12 years and instead get 13. Or you look at people who were going to get 8 years and instead get 9. It does not mean that they are measuring the cumulative impact of multiple years of schooling.
The paper even addresses this point directly: “The finding of educational effects on intelligence raises a number of important questions that we could not fully address with our data. First, are the effects on intelligence additive across multiple years of education?”
So the paper says “one extra year of schooling is worth 1-to-5 IQ points.” Then the tweet changes that to “every year of schooling is worth 1-to-5 IQ points.” A small change, but it distorts the meaning in a way that (inadvertently) sensationalizes the results.
Maybe this isn’t the biggest deal, but it was interesting to me to see how really good work gets summarized in ways that subtly change its meaning.
Getting back to my original skepticism, it was from the large spread on effect size combined with the “every year” misstatement. I’m now less skeptical about the study, per se, but I think that it’s only a start.
I think “a year of education” is at best a weak proxy for the true cause. There are surely some types of education that improve reasoning ability, but maybe the variance in the estimate hints that the kind of education matters (and not just the quality).
And, what do you know, the paper authors agree: “Finally, what are the underlying psychological mechanisms of the educational effect on intelligence?” It’s their final area for more study, and, I think, the most important!
Also, obviously the biggest problem with all of this is that the whole concept of IQ testing is fundamentally flawed. See Radiolab’s excellent “G” for a good primer.