What is IQ — and how much does it matter? (2024)

Earlier this year, 11-year-old Kashmea Wahi of London, England scored 162 on an IQ test. That’s a perfect score. The results were published by Mensa, a group for highly intelligent people. Wahi is the youngest person ever to get a perfect score on that particular test.

Does her high score mean she will go on to do great things — like Stephen Hawking or Albert Einstein, two of the world’s greatest scientists? Maybe. But maybe not.

IQ, short for intelligence quotient, is a measure of a person’s reasoning ability. In short, it is supposed to gauge how well someone can use information and logic to answer questions or make predictions. IQ tests begin to assess this by measuring short- and long-term memory. They also measure how well people can solve puzzles and recall information they’ve heard — and how quickly.

Every student can learn, no matter how intelligent. But some students struggle in school because of a weakness in one specific area of intelligence. These students often benefit from special education programs. There, they get extra help in the areas where they’re struggling. IQ tests can help teachers figure out which students would benefit from such extra help.

IQ tests also can help identify students who would do well in fast-paced “gifted education” programs. Many colleges and universities also use exams similar to IQ tests to select students. And the U.S. government — including its military — uses IQ tests when choosing who to hire. These tests help predict which people would make good leaders, or be better at certainspecific skills.

It’s tempting to read a lot into someone’s IQ score. Most non-experts think intelligence is the reason successful people do so well. Psychologists who study intelligence find this is only partly true. IQ tests can predict how well people will do in particular situations, such as thinking abstractly in science, engineering or art. Or leading teams of people. But there’s more to the story. Extraordinary achievement depends on many things. And those extra categories include ambition, persistence, opportunity, the ability to think clearly — even luck.

Intelligence matters. But not as much as you might think.

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Measuring IQ

IQ tests have been around for more than a century. They were originally created in France to help identify students who needed extra help in school.

The U.S. government later used modified versions of these tests during World War I. Leaders in the armed forces knew that letting unqualified people into battle could be dangerous. So they used the tests to help find qualified candidates. The military continues to do that today. The Armed Forces Qualification Test is one of many different IQ tests in use.

IQ tests have many different purposes, notes Joel Schneider. He is a psychologist at Illinois State University in Normal. Some IQ tests have been designed to assess children at specific ages. Some are for adults. And some have been designed for people with particular disabilities.

But any of these tests will tend to work well only for people who share a similar cultural or social upbringing. “In the United States,” for instance, “a person who has no idea who George Washington was probably has lower-than-average intelligence,” Schneider says. “In Japan, not knowing who Washington was reveals very little about the person’s intelligence.”

Questions about important historical figures fall into the “knowledge” category of IQ tests. Knowledge-based questions test what a person knows about the world. For example, they might ask whether people know why it’s important to wash their hands before they eat.

IQ tests also ask harder questions to measure someone’s knowledge. What is abstract art? What does it mean to default on a loan? What is the difference between weather and climate? These types of questions test whether someone knows about things that are valued in their culture, Schneider explains.

Such knowledge-based questions measure what scientists call crystallized intelligence. But some categories of IQ tests don’t deal with knowledge at all.

Some deal with memory. Others measure what’s called fluid intelligence. That’s a person’s ability to use logic and reason to solve a problem. For example, test-takers might have to figure out what a shape would look like if it were rotated. Fluid intelligence is behind “aha” moments — times when you suddenly connect the dots to see the bigger picture.

Aki Nikolaidis is a neuroscientist, someone who studies structures in the brain. He works at the University of Illinois at Urbana-Champaign. And he wanted to know what parts of the brain are active during those “aha” episodes.

In a study published earlier this year, he and his team studied 71 adults. The researchers tested the volunteers’ fluid intelligence with a standard IQ test that had been designed for adults. At the same time, they mapped out which areas of test takers’ brains were working hardest. They did this using a brain scan called magnetic resonance spectroscopy, or MRS. It uses magnets to hunt for particular molecules of interest in the brain.

As brain cells work, they gobble up glucose, a simple sugar, and spit out the leftovers. MRS scans let researchers spy those leftovers. That told them which specific areas of people’s brains were working hard and breaking down more glucose.

People who scored higher on fluid intelligence tended to have more glucose leftovers in certain parts of their brains. These areas are on the left side of the brain and toward the front. They’re involved with planning movements, with spatial visualization and with reasoning. All are key aspects of problem solving.

“It’s important to understand how intelligence is related to brain structure and function,” says Nikolaidis. That, he adds, could help scientists develop better ways to boost fluid intelligence.

Personal intelligence

IQ tests “measure a set of skills that are important to society,” notes Scott Barry Kaufman. He’s a psychologist at the University of Pennsylvania in Philadelphia. But, he adds, such tests don’t tell the full story about someone’s potential. One reason: IQ tests favor people who can think on the spot. It’s a skill plenty of capable people lack.

It’s also something Kaufman appreciatesas well as anyone.

As a boy, he needed extra time to process the words he heard. That slowed his learning. His school put him into special education classes, where he stayed until high school. Eventually, an observant teacher suggested he might do well in regular classes. He made the switch and, with hard work, indeed did well.

Kaufman now studies what he calls “personal intelligence.” It’s how people’s interests and natural abilities combine to help them work toward their goals. IQ is one such ability. Self-control is another. Both help people focus their attention when they need to, such as at school.

Psychologists lump together a person’s focused attention, self-control and problem-solving into a skill they call executive function. The brain cells behind executive function are known as the executive control network. This network turns onwhen someone is taking an IQ test. Many of the same brain areas are involved in fluid intelligence.

But personal intelligence is more than just executive function. It’s tied to personal goals. If people are working toward some goal, they’ll be interested and focused on what they are doing. They might daydream about a project even while not actively working on it. Although daydreaming may seem like a waste of time to outsiders, it can have major benefits for the person doing it.

When engaged in some task, such as learning, people want to keep at it, Kaufman explains. That means they will push forward, long after they might otherwise have been expected to give up. Engagement also lets a person switch between focused attention and mind wandering.

That daydreaming state can be an important part of intelligence. It is often while the mind is “wandering” that sudden insights or hunches emerge about how something works.

While daydreaming, a so-called default mode network within the brain kicks into action. Its nerve cells are active when the brain is at rest. For a long time, psychologists thought the default mode network was active only when the executive control network rested. In other words, you could not focus on an activity and daydream at the same time.

To see if that was really true, last year Kaufman teamed up with researchers at the University of North Carolina in Greensboro and at the University of Graz in Austria. They scanned the brains of volunteers using functional magnetic resonance imaging, or fMRI. This tool uses a strong magnetic field to record brain activity.

As they scanned the brains of 25 college students, the researchers asked the students to think of as many creative uses as they could for everyday objects. And as students were being as creative as possible, parts of both the default mode network and the executive control network lit up. The two systems weren’t at odds with each other. Rather, Kaufman suspects, the two networks work together to make creativity possible.

“Creativity seems to be a unique state of consciousness,” Kaufman now says. And he thinks it is essential for problem-solving.

Turning potential into achievement

Just being intelligent doesn’t mean someone will be successful. And just because someone is less intelligent doesn’t mean that person will fail. That’s one take-home message from the work of people like Angela Duckworth.

She works at the University of Pennsylvania in Philadelphia. Like many other psychologists, Duckworth wondered what makes one person more successful than another. In 2007, she interviewed people from all walks of life. She asked each what they thought made someone successful. Most people believed intelligence and talent were important. But smart people don’t always live up to their potential.

When Duckworth dug deeper, she found that the people who performed best — those who were promoted over and over, or made a lot of money — shared a trait independent of intelligence. They had what she now calls grit. Grit has two parts: passion and perseverance. Passion points to a lasting interest in something. People who persevere work throughchallenges to finish a project.

Duckworth developed a set of questions to assess passion and perseverance. She calls it her “grit scale.”

In one study of people 25 and older, she found that as people age, they become more likely to stick with a project. She also found that grit increases with education. People who had finished college scored higher on the grit scale than did people who quit before graduation. People who went to graduate school after college scored even higher.

She then did another study with college students. Duckworth wanted to see how intelligence and grit affected performance in school. So she compared scores on college-entrance exams (like the SAT), which estimate IQ, to school grades and someone’s score on the grit scale. Students with higher grades tended to have more grit. That’s not surprising. Getting good grades takes both smarts and hard work. But Duckworth also found that intelligence and grit don’t always go hand in hand. On average, students with higher exam scores tended to be less gritty than those who scored lower.

But some people counter that this grit may not be all it’s cracked up to be. Among those people is Marcus Credé. He’s a psychologist at Iowa State University in Ames. He recently pooled the results of 88 studies on grit. Together, those studies involved nearly 67,000 people. And grit did not predict success, Credé found.

However, he thinks grit is very similar to conscientiousness. That someone’s ability to set goals, work toward them and think things through before acting. It’s a basic personality trait, Credé notes — not something that can be changed.

“Study habits and skills, test anxiety and class attendance are far more strongly related to performance than grit,” Credé concludes. “We can teach [students] how to study effectively. We can help them with their test anxiety,” he adds. “I’m not sure we can do that with grit.”

In the end, hard work can be just as important to success as IQ. “It’s okay to struggle and go through setbacks,” Kaufman says. It might not be easy. But over the long haul, toughing it out can lead to great accomplishments.