- In popular culture, the
term IQ is everywhere. - Do IQ exams do that? - You probably need 120 points of IQ. - Don't know what my IQ is. - And IQ. - IQ.
- IQ. - Low IQ individual. - People who boast about
their IQ are losers. - When people say IQ, what they mean is intelligence, an objective, rigorous measurement
of intellectual ability. But does it actually work? Well, in this video, I want to find out: Where IQ came from. What does it actually measure? What can it predict about your life? And I guess, what is my IQ? I have never taken an
official IQ test before. Honestly, I don't think
I'm terribly smart. I've always kind of considered my IQ to be maybe just a little above average. - Exothermic or endothermic? - I feel like that should be exothermic. - Good job, science guy. - There are a lot of IQ tests online, but I am very skeptical
about their accuracy. Still, I figured some of
them may be good practice for the real thing. Tomorrow I'm going to
do an IQ test for real. Before I do that, I want
to try to improve my score, and so I'm going to try to do a
whole bunch of practice tests. I think this test is trainable. But tomorrow we're going to
see whether that's true or not. The idea of intelligence testing goes back hundreds of years, but the first concrete
breakthrough occurred in 1904. English psychologist Charles Spearman was studying students'
grades in different subjects and he wondered how their
performance in one subject, like English, would relate
to their performance in another, like Math. One option would be that the
better a student did in math, the worse they would do in English, maybe because they spent
more time on their math work and so had less time to devote to English. So performance in different subjects would be negatively correlated. Another option was that
performance in one subject would be completely unrelated
to performance in another. After all, different subjects
require different skill sets, so maybe marks would be
totally uncorrelated. The third option was that the
better a student did in math, the better they would do in English. In other words, their marks
would be positively correlated. A correlation coefficient can vary anywhere from negative
one to positive one. A correlation coefficient of negative one indicates a perfect negative correlation, meaning an increase in
one variable corresponds to a precise, predictable
decrease in the other variable. Similarly, a correlation of positive one indicates a perfect positive correlation. A correlation of zero indicates no relationship between the two variables. And any value between zero and one indicates a positive correlation, but the data has some random spread. The square of the correlation coefficient tells you the amount of
variation in one variable that can be explained by
variation in the other variable. For example, if the
correlation coefficient is 0.5, then 25% of the variation in one variable can be explained by the other. When Spearman analyzed his data, he found a clear positive correlation. Students who did better in math also tended to do better in English, and the correlation coefficient was 0.64. But Math and English
weren't the only subjects the students studied. They also took Classics and French. And when Spearman looked
at the correlations between all of these subjects,
he found the same pattern. Students who did well in one subject tended to do well in them all. So how do you explain this observation? Well, Spearman proposed that each person has some
level of general intelligence, what he called the g-factor. This construct was meant
to capture how quickly students could learn new
material, recognize patterns, and think critically regardless
of the subject matter, which explains why students' scores across subjects are correlated. Those with high g, score
well on all subjects and those with low g, score
poorly on all subjects. Spearman published his
conclusions in a paper titled "General Intelligence" Objectively
Determined and Measured. But the correlations weren't perfect. So on top of the g-factor, Spearman proposed subject-specific
factors, or s-factors. A student's performance
in math, for example, would depend on their general intelligence plus their subject
specific factor for math. Subject specific factors could increase or decrease performance on
that particular subject. Spearman believed that specific
factors could be trained but general intelligence was fixed. So he wanted to find a
way to reliably measure general intelligence. At around the same time in France, Alfred Binet was tasked with figuring out which kids needed more help in school. Together with Theodore Simon, he developed the Benet-Simon test. Students were asked to name
what's missing in the drawing, define abstract terms,
and repeat back sentences. And there was also this question asking which face is prettiest. There were 30 tasks in all. Their performance was benchmarked against other students of different ages in order to assign them a mental age. For example, if a student performed about as well as the
average eight year old, their mental age would be eight. This mental age was then
divided by their actual age and multiplied by a hundred to arrive at a so-called intelligence
quotient, and IQ was born. So the Binet-Simon test was
the world's first IQ test. It was translated by Goddard into English and brought to the U.S. At Stanford, Lewis Terman standardized it using a large American sample, and with some modifications it became the Stanford-Binet test, and for decades it was
the most widely used test in the United States. But this was just the start. Many other IQ tests were developed and they all had the same goal
of measuring the g-factor. The way they did this was by assessing many different mental abilities, including memory, verbal,
spatial, and numerical skills. Each one of these areas might
have a subject-specific shift. But by averaging them all together, the idea was the subject-specific
effects would cancel out, leaving a decent approximation of g. Of course, there would
always be some error. But that's why psychologists
designed IQ tests with upwards of seven to 10
sections with distinct tasks to try to minimize
subject-specific distortions. All the different IQ tests differed in the number of questions
and their difficulty. So to standardize the scoring system, each test was given to a large
sample of the population. Raw scores were normalized, usually so the mean was a hundred and the standard deviation was 15, and that's how it's
still done to this day. This is known as IQ, and it's meant to be a measure
of an individual's g-factor in comparison to the
rest of the population. The way it's scaled, 68% of people have an
IQ between 85 and 115. Only around 2% score over 130 or under 70. (tranquil music) 11 lions, four cats, and
seven crows have a total of... Oh, boy. As I was studying for my IQ test, I practiced all the
different types of questions that appear on modern tests. One section will almost
certainly be on vocabulary. They give you one word like sanguine, and you have to pick which of
the multiple choice options is most similar in meaning. Is it gloomy, asinine, recalcitrant, optimistic, or reflective? They might also ask you to pick a word with the opposite meaning. So what is the opposite of perspicacious? Is it canny, obsequious,
dull, fanciful, or sagacious? Another section tests your ability to spot patterns with numbers. So pick the number that
best completes the pattern. 3, 5, 8, 12. What comes next? Originally, I was looking
for complicated patterns, but as I familiarized myself
with the online tests, I discovered the patterns
were usually pretty simple. A good technique is to find the difference between adjacent terms. So in this case, the first two
terms are separated by two, the next by three, and then four. So the logical next term should
be five more than 12, so 17. The answer is C. Sometimes the numbers grow rapidly, like in the sequence three, 15, 60, 180. What comes next? In cases like this, I look at the ratio of one
number to the one before it. In this case, the second
number is five times the first. The next number is four times bigger, and the next one is three times larger. So the answer should be
two times the fourth term, which is 360, answer B. One of the best known
types of IQ test questions are Raven's progressive matrices. These involve a three by three grid with symbols in each of the cells, and you have to select the ninth cell which follows the pattern. I found that the bulk of these puzzles obey one of only a few
different logical rules. One is translational motion. So the symbols move from
one cell to the next in a predictable fashion. The second is rotational motion. One or several objects rotate
from one cell to the next. The third is missing symbols, where in each row or column
each symbol appears once. So to figure out which symbols
appear in the final cell, you just have to spot
which ones are missing. And the fourth is addition, where the first cell plus the second cell equals the third cell. In this case, lines
that overlap cancel out, but a line plus nothing equals a line. In most modern IQ tests, all the questions are
completed under time pressure. You may have only around 10
to 30 seconds per question. Okay, this morning I'm
taking an official IQ test, and I got to say that I'm pretty nervous. I always want to do well on tests, it's something I pride myself on. But at the same time, who
knows how this is going to go. I'm not allowed to take you in there, because obviously people don't want the questions getting out, and they don't even want video of what it looks like in there. They're very strict about these things. So I'm going to go in, do the test, I'll come out and I'll
let you know how it went. Wish me luck. What's remarkable about IQ tests is that an hour or two of
questions on vocabulary, numbers, and arbitrary shapes can predict a surprising
amount about your life. For one thing, the higher your IQ, the larger your brain is likely to be. A large meta-analysis from 2005 estimated a correlation of
0.33 between IQ and brain size. So high IQ is literally big brain. IQ is also predictive of school success. In 2007, Scottish psychiatrist Ian Deary measured the IQs of 13,000 11 year-olds. And five years later, when
these students completed national school examinations, Deary compared their
exam marks to their IQs. - Their performance on an
IQ test when they were 11 correlated with their performance five years later on the GCSEs, about 0.8. That's an extremely high correlation. - It means about two
thirds of the variation in national school examination scores could be predicted by IQ
tests taken five years prior. Now, the correlation
coefficient of this study is at the high end of the 0.2 to 0.8 range found in similar studies. But research supports the claim that IQ is a good predictor of school success. It also predicts how much
schooling a person will complete. Maybe this shouldn't be so surprising since some school tests
are essentially IQ tests. It's been argued that tests
like the SAT, ACT, and the GRE are basically IQ tests. They correlate with standard
IQ tests at around 0.8. Now, on my SATs I got a score of 1,330, which of corresponds
to an IQ of around 130. So it'll be interesting to see if my official IQ score matches that, or if I was able to increase my score by familiarizing myself
with IQ-style questions. I don't know. But IQ also has predictive
power outside of school. One of the most robust findings is that IQ can predict job success. - Particularly in technical
or high complexity jobs. - How do you measure occupational success? - You ask people's bosses to rate them. You ask what people's income is. You measure productivity
in ways that economists use about the output generated. - The correlations typically
range from 0.2 to 0.6, and the effect is most
notable for more complex jobs, which makes sense. The highest effect is
for military training. In fact, the U.S. military
will not accept anyone with an IQ under 80. They also limit to 20%
the number of recruits with IQs between 81 and 92. During the Vietnam war, in order to increase
the pool of applicants, they relaxed this last requirement. But what they found was that
those below the threshold were 1.5 to three times as
likely to fail recruit training, and they required between
three to nine times as much remedial training. Taken together, this added so much strain that the military ran more efficiently without the extra recruits. In total, 5,478 people recruited
under this initiative died at a fatality rate three times higher than ordinary recruits. So the military reinstated
their requirements, and today anyone with an IQ less than 80, that is about 30 million Americans, would be ineligible to join the military. Even outside the military, IQ seems to play a role
in how long you live. In a Scottish study, scientists uncovered IQ tests from kids when they were 11 years old. Now 65 years later, they check
to see who from the sample was still alive at age 76. And they found that on average, for every 15 point
increase on the IQ test, you would be 27% more likely
to still be alive at age 76. A large meta-analysis confirms that people with higher IQs
have a lower risk of dying during the timeframe
investigated in each study. The last major thing that IQ
seems to predict is income. This study shows a clear tendency for income to increase with IQ, and it found a correlation
coefficient of 0.3. But the variance is huge. In fact, the top three
earners in this study all had IQs below 100. A large meta-analysis of 31 studies found the correlation between
IQ and income to be 0.21. That is significant but small. It means that only 4.4%
of the variance in income is explained by IQ. Maybe one of the reasons why we don't see as high a correlation for income is just because economically intelligence is not necessarily
that highly rewarded, in that maybe there are jobs, like just doing a real estate-type scheme, maybe that doesn't require a
huge amount of intelligence. Simultaneously, you have all these very highly intelligent people who maybe become college professors, but that doesn't
necessarily pay very well. - Yeah. - A lot of people who have
very high intelligence scores don't have the same interest
in accumulating money. - The relationship with
net worth is even weaker. It hardly seems to correlate with IQ, even though people with higher IQs are supposedly more intelligent and on average they make
more money each year. But this apparently doesn't translate into saving or accumulating
more wealth overall. But if IQ correlates
with school achievement, job performance, income, and longevity, why don't we hear more about it? Why aren't more people tested? I think it's because
IQ has a dark history. When Henry Goddard brought
Binet's test to America, its use and interpretation
shifted dramatically. In France, Binet believed intelligence could be improved through education. He designed his tests so
that struggling students could be given more help to catch up. But in the U.S., the modified
test was given to adults to rank them by intelligence. And researchers like Spearman believed that g was unchangeable, that whatever general
intelligence you were born with you would have for the rest of your life. And many thought g was inherited, passed down from parents to children. These days we would say
it has a genetic basis. There is some evidence to
support these assertions. IQ appears fairly consistent
over one's lifetime. - So they had tests done when
people were 11 years old. They found all those
tests in a filing cabinet and followed those people up and gave them the same test
when they were 90 years old, much, much later. - Their scores 80 years apart were correlated at around 0.5 to 0.6. There's also evidence for
a genetic basis to IQ. - You find, for instance, that if you get two identical twins and give them an IQ test, they have a very strong correlation. It's actually about the same as giving the same person
the test a few weeks apart. - Henry Goddard used the claims that intelligence was
inherited and unchangeable to put IQ at the center of the
American eugenics movement. Eugenicists wanted to prevent
those with undesirable traits from having kids. In many states, laws were passed to enable forced sterilization of people who failed to meet a certain
threshold on an IQ test. The constitutionality of these laws was upheld by the Supreme Court in 1927. - Even words that we
now use as in insults, moron, idiot, imbecile, were
used as scientific terms. - In his judgment, Justice
Oliver Wendell Holmes wrote, "It is better for all the world if instead of waiting to execute degenerate offspring for crime, or to let them starve
for their imbecility, society can prevent those
who are manifestly unfit from continuing their kind. Three generations of
imbeciles are enough." In total, over 60,000 people
were forcibly sterilized as a result of these laws. In fact, they served as
a model for Nazi Germany. Hitler himself claimed to be inspired by American eugenicists. - These have been used for
horrific things in the past. - At the Nuremberg trials after the war, some Nazis quoted from the
American Supreme Court decision. Given this awful history, I think it's understandable
that many people completely disregard IQ today. On the science of intelligence,
there are a number of things those early researchers got wrong. One is that IQ is not entirely
determined by genetics. Can you quantify the effects
of genetics versus environment? - When you look at twin studies, on average, across the whole
lifespan, it's about 50/50 to heritability and environment. - You simply can't, for ethical reasons, estimate it in humans with a reasonable degree
of certainty or accuracy. Given my reading of that literature, it's a pretty broad range, probably somewhere between 40% and 70%. - Okay. And since education can improve IQ, it is not completely
fixed over a lifetime. Plus, intelligence might
not be a single construct as initially imagined. These days, scientists recognize
two forms of intelligence, fluid and crystallized. Fluid intelligence is
your ability to learn, process information, and
solve novel problems. Whereas crystallized intelligence involves the knowledge you've
accumulated over your lifetime. Both types of intelligence
increase throughout childhood, but fluid intelligence
peaks in early adulthood and then declines. Whereas crystallized
intelligence remains more stable. But IQ has been further misused to promote the idea of racial
differences in intelligence. There is, for example, an observed gap between the average IQ of
black and white Americans. Articles have also been
published on the IQs of different nations around the world. Many of these nations
are purported to have average IQs below 70. That's the cutoff for
intellectual disability. How could this be? The conclusion that some draw is that there are genetic differences between races or nations in intelligence. But I think that's a gross
misrepresentation of the data. The problem, I'd argue, is that IQ tests don't necessarily measure what
you think they're measuring. And the proof is that there's
a representative sample of white Americans whose average IQ is 70. Who are these people? Just ordinary Americans who lived around a hundred years ago. Researcher James Flynn
studied the average results of IQ tests over the past century, and every so often, the tests
get updated and re-normalized to keep their average at a hundred. Now, what Flynn noticed was that each time they got re-normalized, the scores had to be
shifted down a bit more by about two or three
IQ points per decade. And if they didn't do
this, what we would see is that the average IQ
of the whole population was increasing at a steady rate for the last a 100 years, adding up to around a 30 point increase. This is known as the Flynn Effect. - Were our immediate ancestors on the verge of mental retardation? Because 70 is normally the
score for mental retardation. Or are we on the verge
of all being gifted? Because 130 is the cutting
line for giftedness. - Now the genetics of the population haven't really changed
over a hundred years. So what caused the increase? Well, there is some debate
about the true causes, but one of them is probably improving childhood nutrition and health. - You know, height also increased
across that time period. People got taller, and taller, and taller. - Another cause is better education. - There's lots of evidence that school makes you more intelligent. - You become better at problem solving if you have more knowledge. Because it's easier for
you to make associations if you have more things to
make the associations with. - A third proposed cause is a shift in the types of work that most people do, from mostly manual labor
a hundred years ago, to much more abstract thinking these days. And that shift may have made us better at answering the types of questions that are asked on IQ tests. Rotate again. The point is that IQ tests appear to objectively measure
intelligence, but they don't. Even in the same country,
separated only by time, cultural changes can affect
the average scores on IQ tests. So why shouldn't we expect
cultural differences between groups at the same
time to have the same effect? Some tests go so far as to
label themselves culture fair, meaning the questions
should be equally valid for all cultures. But the truth is it's impossible
to construct such a test. Does that work? - No. - Okay. - No. I mean, that's just a title, right? That's just a marketing term. I don't think there is such a thing as a completely culture
free or culture fair test. - Culture fair tests
assess visual relations, geometric shapes and patterns, ignoring the fact that cultures differ in, for example, whether they
have words for shapes or spatial relations. These differences influence
how people think about and use categories. It's also debatable whether cultures without printed materials
even perceive them in the same way that we do. What culture fair tests don't assess is ethnobotanical knowledge,
or training dogs to hunt, or surviving alone in the rainforest. Arguably, these forms of intelligence are more important for survival than knowing, say the next
number in the sequence. But since they're less
common in our culture and we don't have good
ways of measuring them, we see IQ puzzles as the definitive way to quantify intelligence. And the people who make these tests agree. There are stringent
requirements before a test validated for one population can be used with a very
different population. Even in the limited forms of intelligence that IQ attempts to assess, there are factors other than
g which affect the final IQ, like motivation. How much someone is incentivized
to complete the test can have a marked impact on their score. Many studies have tried paying subjects to complete an IQ test. In some studies, they're offered a little, say around a dollar. Other studies offer between $1 and $10. And the real high rollers
offer more than $10. A large meta-analysis showed
that motivating people in this way increased IQ. And the larger the dollar amount, the greater the average increase. At the high end, IQ
increased by up to 20 points. The effect is largest for
those with below average IQs. So in addition to g, IQ tests
also measure motivation. But it doesn't stop there. They do rotate. Training and coaching for an IQ test can boost scores by up to eight points. I just completed the test
in some random notice. (mumbles) I can barely talk after that. It seemed pretty fair. There were lots of different sections. The math section in particular,
I feel like I killed. Those questions were easy. I would say having done the test, I feel like that should be trainable, like you should be able to
train someone to do that well. Test taking strategy is also important. Some people are just
better at taking tests under time pressure than others. I think the hardest thing about the test was the time limits. Looking for the patterns
in a series of shapes, I mean, it just normally
takes me a little while, and so I feel like I didn't finish those. You have to know when to skip questions, how to eliminate clearly wrong
answers, and when to guess. Anxiety also plays a role. Apparently a small amount
of anxiety is good, but past a certain point, it
negatively impacts performance. I guess the overall review
is, I think I did okay, and I think the training
actually really, really helped. That's my prediction. Let us fast forward to the future and see how I actually did. I actually got my results from the author of the IQ test I took. - Those are three areas,
three specific areas. - For the math one, for the numbers ones, I think that's where I
felt really comfortable, and got there before the time was done and then I could go back
and look at a few things. - Yes. You blew the roof off
the quantitative one. On the quantitative, it was 143. Whereas on the crystallized
intelligence index, it was 132. The fluid intelligence index was 118. - Hmm.
- Which still is a higher score than 88.5%. - It's not, bad. But it's interesting that that one is significantly lower, I guess. - And that's not an unusual difference. Around that concept of g, people have strengths and weaknesses. If we were to look at the
best estimate of g for you on this set of tests. And it'd be different if
you took a different test. It was at 134, which is higher
than 98.8% of the population. - Wow. - Hopefully you're not
disappointed with any of that. - No. I wanted to do well. I feel like my motivation was high, possibly higher than the average person. So what is IQ good for? - My clinical practice now
is forensic neuroscience, and about 90% of my
cases are death penalty. One of the most common issues is what's referred to as the Atkins defense after the name of the
US Supreme Court case that eliminated the death penalty for people with intellectual disability. - Can't the criminal
just throw the IQ test? Can't they just intentionally - No.
- answer every question wrong? - We'd know that. I mean, we include, just like
in the test that you took, there are embedded measures of invalidity. It's detected using various
mathematical algorithms. We're better than 95% accurate in detecting people who are attempting to fake poor performance. - Oh, wow. - One thing that we may
be interested in doing is to boost people's cognitive
ability early in life so that it takes them, even if they go into cognitive decline, it takes them longer to reach the point where they'll have sort of functional actual everyday problems
where they lose independence, whether it comes to
dealing with their money, or whether it comes to
dealing with reading labels, whatever it is that people struggle with when they get into later
stages of cognitive decline. If we could discover a way to lastingly boost people's intelligence, that would be massively helpful. - Maybe its best use is
in identifying individuals with strong intellectual abilities who haven't otherwise been
able to demonstrate them. - Teachers would recommend that a kid gets put in the
gifted and talented program, because generally they'd observed them doing well in the classroom. But if you replace that
with a standardized test, an IQ test, you find a higher
proportion of poorer kids and kids from minority ethnic backgrounds in the gifted and talented
program when you use an IQ test. And the reason is that you're
using an objective measure. You're not just relying
on some teacher's opinion. Getting into a good school
was about who you knew, or who your parents knew, or how much money your parents had, not so much about how you were doing. The idea that you could try to develop an objective-ish measure
that would try and iron out all those social biases was
clearly a well-meaning idea. - IQ is something that
not only psychology, but the general public has a
love-hate relationship with. - Tell me about that. - Psychologists hate to
talk about intelligence and people's intelligence test
scores and that kind of stuff. And I've had parents, when
I've included intelligence as part of a neuropsychological
evaluation of their kid, they'll say, "Well, yeah,
I'd like to know his IQ, but you know, we don't
really care about that. What was it?" (both laughing) - And then I also think you
have the debate about IQ, extremes on both sides,
which I think doesn't help. You have the extreme of people who say this is the most important thing ever, people's IQ is a majorly important factor that we must know about them, and then we can classify
them into particular schools, or particular ways of
education or whatever. That's a one extreme, and I think that's totally unproductive. But there's another extreme. The other extreme is the
kind of blank slate view, which is that these tests
are completely useless, they don't tell us anything, that they're only a tool of
racism and prejudice and so on. I think that's wrong as well. And there's just this massive firestorm on both sides happening around them. And the people in the
middle just get forgotten, the people have more moderate
views on these sort of topics. So I'd recommend that people look for the more moderate views on this. - I think the big mistake
is thinking that IQ in some way determines someone's worth. What's much more important, in my opinion, is how you interact with and
help the people around you. Which is why I think Stephen Hawking said, "People who brag about
their IQ are losers." While IQ tells us something, it doesn't tell us how
our lives will turn out. We have the ability to
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