The Strangest Things that Correlate with IQ
- Spencer Greenberg
- 12 minutes ago
- 9 min read
Short of time? Read the key takeaways.
🧠 IQ measures a specific kind of cognitive ability, not overall human worth. IQ summarizes performance across a wide range of cognitive tasks (e.g., logic, vocabulary, mathematics) into a standardized score. It does not directly measure social skills, morality, wisdom, or practical abilities outside the kinds of tasks found on intelligence tests.
🔍 Higher IQ is linked to some surprising traits and behaviors. People with higher IQs tend to be better at spotting pseudo-profound nonsense, slightly more likely to be firstborn or nearsighted, and less likely to believe they can easily solve society's biggest problems.
🌱 Health and environment may play an important role in cognitive ability. Factors such as lead exposure, sleep apnea, high blood pressure, hearing loss, head injuries, and poor childhood nutrition are all associated with lower IQ or cognitive decline, though not all of these relationships are necessarily causal.
🗳️ IQ is associated with some beliefs and attitudes. On average, higher-IQ people are less likely to be religious and more likely to support free speech for people they disagree with, though the reasons for these associations remain uncertain.
📚 Practice matters far more than IQ for most real-world skills. You don't need a higher IQ to become excellent at something—deliberate practice, effective learning, and good feedback can produce enormous improvements in performance.
⚖️ IQ predicts many interesting outcomes, but it is far from everything that matters. IQ is scientifically meaningful because it correlates with a wide range of life outcomes, yet it has little relationship with happiness or conscientiousness, reminding us that intelligence is only one ingredient of a successful life.
When you think about IQ, you might think about scientists like Einstein, or about nerds who'd rather read an academic paper than talk to another human being. But, in this article, I'm going to tell you about some of the strangest things that have been found to correlate with IQ, including in our own giant IQ study involving over 3,000 people, and in the work of other researchers. If you prefer, you can instead watch our video on this subject (or you can go even deeper with our full research report):
So, what is IQ? Well, it's a standardized score that's designed to test cognitive ability. Essentially, it measures what intelligence tasks conducted in a lab have in common. So, if you give people a wide range of intelligence tasks, let's say logic puzzles, math, spelling, vocabulary, and then you calculate a score that best predicts people’s performance at all of these different tasks, that's a measure of IQ (once it's standardized). Typically, IQ is standardized based on a population so that 100 is the average score, and the standard deviation (how "wide" the distribution is) is 15. IQ doesn't necessarily predict how good you are socially or morally, or whether you're good at the sort of things that hunter-gatherers tended to be good at. If you want to learn more, we have written another article that goes into more detail about what intelligence tests measure.
Now that we have a handle on what IQ is, let's jump into some of the strangest findings about what correlates with it.
1) Pseudo-profound bullshit
Now, as we all know, a formless void serves the mechanics of destiny and interdependence is an unparalleled element of all experience.
But wait, that statement is actually total pseudo-profound bullshit. And fascinatingly, in our study, when we gave people statements like these and asked them to rate how profound they are, higher IQ people tend to rate them as less profound. In other words, they seemed better at calling out bullshit, on average.
Relationship between IQ and profoundness ratings (both variables controlled for age, gender, and data source). Source here.
Perhaps this is because people with higher IQs are less likely to assume that just because they don't understand something, it's actually meaningful. If you watch certain questionable intellectuals on podcasts, you'll actually see this quite a bit: they'll say something that sounds profound but doesn't really have any meaning, and the audience, not understanding it, assumes that it must be really deep and gives the benefit of the doubt. When you hear things like this, I recommend deep diving and saying, "Well, what does this mean, really?" If you break it down carefully and still can't figure out the meaning, yet it's been intended for a general audience (rather than being technical on purpose, such as physicists discussing physics), there's a real chance that the original statement is pseudo-profound bullshit.
2) Birth order
As the second child born in my family, I find this next one especially interesting. IQ is actually associated with being the firstborn child. It's debated why this is, but one theory is that it has to do with parental investment: If you only have one child, you can devote more time to raising them. Time-use surveys suggest that this might actually be the case, that parents put more time into raising their firstborn child. So perhaps this extra parental investment leads a child to have a higher IQ over time.
We're not talking about a huge difference here. We're just talking about a few IQ points, but it's interesting that there's a difference at all.
3) Intellectual hubris
Next, I want to tell you about one of the funniest correlations we found in our giant study of IQ.
Who do you think has higher IQs on average:
People who believe they can figure out solutions to societal problems
People who believe they can't figure out solutions to societal problems
Well, it turns out that in our study, people who believe they can't figure out solutions to societal problems actually tended to have higher IQs. Perhaps because they were more aware of how incredibly difficult it is to figure out those kinds of solutions.
You might think that the explanation for this is the Dunning-Krueger effect.
An example of how the Dunning-Krueger effect is purported to appear,
People sometimes mistakenly think that the Dunning-Krueger effect is that lower-skilled people think that they're better than higher-skilled people, but that's actually not what it is. The Dunning-Krueger effect says that lower-skilled people tend to overestimate their ability, not that they tend to think their ability is higher than that of higher-skilled people. So this is different from the Dunning-Krueger effect. (If you’d like to know more about the Dunning-Kreuger effect, including some reasons to be skeptical about it, you can see our article about that, here.)
4) Wearing glasses
There's a stereotype that nerdy people are more intelligent and more likely to wear glasses. And many people believe that wearing glasses gives you an air of being intelligent. Fascinatingly, though, when a study tested this idea by showing faces of people either with glasses or without, people did not perceive them as being more intelligent when they had glasses.
Mean intelligence ratings as influenced by Stimulus Person and Eyewear Condition.
Source, here.
But perhaps surprisingly, studies actually do find a (small) link between IQ and nearsightedness (such as this one, which found that people with higher IQ scores were slightly more likely to be nearsighted, although IQ explained only about 1–2% of the variation in vision). In other words, people who wear glasses probably do have slightly higher IQs on average.
Scatter plot of refractive error against IQ (both variables adjusted for age and sex) with linear regression line and 95% confidence region [n = 1529]. Source: https://doi.org/10.1038/srep45977
Why on earth would there be a link between IQ and nearsightedness, though?
Well, there are a few different theories. One theory is that nearsightedness is actually linked to the amount of light exposure you get when you're young. So, if higher IQ children are more likely to stay indoors rather than spend outdoor time playing, this could actually possibly explain why they tend to be more nearsighted. Another theory is that nearsightedness is linked to close-up work, such as reading or studying. If that's the case, that could also help explain why higher IQ children tend to be more nearsighted. And yet another theory is that there are "shared genetic factors [that] contribute significantly to the covariance between myopia and intelligence."
5) Can you change your IQ?
So far, the correlations we've talked about might be interesting, but they're not useful. So, are there useful IQ correlations that can help us guide how to live our lives? Well, there are actually useful IQ links that can guide our choices.
Toxins such as lead poisoning, especially in children, have been linked to lower IQs.
Sleep apnea. If you wake up not feeling rested and you snore really loudly, you may want to get checked out by a doctor because sleep apnea is associated with lower cognitive function, but is actually treatable. If you're curious about this for yourself, you can try our free Unique Traits Test, which can screen you for sleep apnea, as well as more than 80 other traits (though only a doctor can give an accurate diagnosis).
High blood pressure is linked to a reduction in IQ over time. Treating high blood pressure is important for multiple reasons, IQ being just one of them.
Perhaps most surprisingly, adult hearing loss. When older adults lose their hearing, it tends to precede reductions in IQ. We don't know for sure that it's causal, but I think it's worth being aware of. And treating your hearing loss is good for other reasons as well.
Head trauma. Concussions can be very serious and may even lower IQ. Wear a helmet when doing dangerous activities where you may hit your head, and wear your seatbelt in cars!
Exercise and nutrition. Getting proper nutrition, especially as a child, likely leads to higher IQs. Higher IQ is also linked to boring but incredibly important things like having a healthy diet and exercising regularly.
A caveat here regarding associations: we can't always be certain about the causal role that these things play. For instance, it's known that worse childhood nutrition is linked to lower IQ, but that could be because of other factors, like maybe childhood poverty is linked both to worse nutrition and to lower IQ. It's always worth remembering that correlation often doesn't imply causation.
All of that being said, I think for a number of these, we have pretty good reason to think that there is a causal role, especially things like head trauma and high blood pressure.
But the most important thing to know about cognitive ability, in my opinion, is that you can get better at absolutely any task you choose simply by practicing it and getting good feedback (the faster and more reliable the feedback, the better). You don't need to improve your IQ in order to get better at anything you care about. Someone who's diligently studied math for 10 years is absolutely going to blow out of the water at math someone who is 10 IQ points higher who hasn't studied math at all.
6) Does IQ correlate with certain beliefs?
What about beliefs? Are there any interesting correlations between IQ and what people believe? Well, fascinatingly, higher IQ people tend to be less religious. It's not known why this is, and there are different theories.
Most people in the world are born into a religion, and most people stay with whatever religion they're born into. So, it's possible that what's going on here is that higher IQ people are simply more likely to question whatever belief system they're born into.
It's also interesting that higher IQ people tend to be more likely to support the free speech of people they disagree with. Even if they oppose what a group stands for, whether it happens to be religious fundamentalists or neo-Nazis, they're more likely to express support for that group being able to express their opinions, hold public demonstrations, and be involved in public debates.
7) What does IQ not correlate with?
What about things that you'd expect to be correlated with IQ, but actually aren't? Well, one of the strangest is that you'd think that people with higher IQs would tend to be happier because they tend to be wealthier, they tend to be better at getting certain types of jobs, and (in theory) they should be able to problem-solve better in their lives. But in fact, there is no link between IQ and life satisfaction or happiness.
Source: our giant IQ study
This is a genuine mystery that nobody has really resolved. If IQ is about being able to use your mind to effectively achieve goals, then why does it fail at getting people the thing that almost everyone wants - namely, happiness?
This shows very clearly that IQ is very far from giving you everything you want in life. It doesn't even mean you'll be happy.
A lot of people also expect that IQ is linked to conscientiousness, diligence, hard work, or being organized. But actually, studies (including our own) tend to find that IQ has either no correlation or a very small negative correlation with traits like these. It might be the case that people who are more conscientious tend to seem smarter. Maybe they're more diligent about studying, maybe they're more likely to stay in school, but the evidence suggests they don't actually have higher IQs.
All of the correlations in this article indicate that those who say “IQ is meaningless” are actually just scientifically wrong. We can see that IQ predicts lots of interesting things. However, IQ is also very far from everything that matters; it can't even predict how happy you are.
If you're interested in using psychology to improve your life, I'd love it if you check out my new book, The 12 Levers. My co-author and I deep dived on over 100 self-improvement books and over 20 types of therapy. And every time they gave a method or technique, we extracted it. And through analyzing all of that, we came to a surprising conclusion: There are only 12 main psychological strategies you can use to improve your life. And in the book, The 12 Levers, we teach you what those strategies are and how to use them. You can buy it now, or consider subscribing to my YouTube channel for more deep dives on psychology every week.