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  • In your lifetime, you have probably stared down any number of ability tests and course

  • exams and PSATs, SATs, ACTs, GREs, GCSEs, whatever you got in your country.

  • Humans, it seems, really get a thrill out of measuring, ranking, and comparing each

  • other's intelligence.

  • Unfortunately, as you saw last week, historically, we have been kind of bad at that.

  • Today, we think of intelligence as determined by a series of factors related to genetics,

  • environment, education, perhaps even randomness itself, some aspects of which may correlate

  • with belonging to a particular social group, and others not.

  • The key here, though, is that we don't fully understand how or how much some of these factors

  • work.

  • How do elements like personal history and conditions like poverty, access to education,

  • stress, even nutrition affect someone's scores on cognitive tests?

  • And if a group of people share some of these conditions, how will they respond--both as

  • individuals and as a group--to certain potentially biased intelligence tests?

  • In the end, the irony is that in our ongoing effort to measure human intelligence, most

  • of what we've learned is simply what we don't know.

  • [Intro]

  • What is a piano?

  • Which one of these things is least like the others?

  • Juice is to glass as hand is to what?

  • Which one of these numbers does not belong in the series?

  • Bernice had x number of jelly beans.

  • She ate one, then gave half of what was left to Bruno, then she ate another and gave half

  • of the remainder to her dog.

  • Now, she only has five beans.

  • How many did she--ahheh uhhhh.

  • These questions are similar to what you'd find on today's most widely-used intelligence

  • tests.

  • The Wechsler Adult Intelligence Scale, or WAIS, and the Wechsler Intelligence Scale

  • for Children, or WISC.

  • Originally published by psychologist David Wechsler in 1955, the current edition of the

  • exam consists of fifteen different sub-tests that assess things like vocabulary, similarities

  • between objects and concepts, and patterns in letters and numbers.

  • Cognitive tests usually fall into one of two categories: achievement, or the kind that

  • reflect what you've learned, and aptitude - the kind that's supposed to predict your

  • ability to learn something new.

  • So the WAIS and the WISC are aptitude tests, and your final exam at the end of your math

  • class is an achievement test.

  • So, how do we know if an intelligence test, or any other test for that matter, is actually

  • any good?

  • Well, today, we do have some standards.

  • To be widely accepted, a test must hit three important marks.

  • It has to be standardized, reliable, and valid.

  • Standardization is basically about comparability.

  • Whether you answer 15 or 50 questions correctly on a test actually means very little until

  • you can compare those scores against how others performed.

  • So, to achieve meaningful comparisons, test-makers must first give the test to a representative

  • sample group, which sets a standard by which to compare future test-takers.

  • You've probably heard of a bell-curve.

  • Whether you're measuring height or mental aptitude or love of the Beatles, it's often

  • assumed that everyone you're measuring will fall into what's called a normal pattern:

  • most scores will fall in the mid-range, while fewer hit the extremes.

  • And actually, it's those extremes that intelligence tests are most widely and effectively used

  • for.

  • It might help an educator identify a gifted student who totally blows the roof off a test,

  • but they're also useful in helping clinicians determine who might have a disability or be

  • facing some specific barrier.

  • With victims of traumatic brain injury or stroke, for example, a WAIS test can do a

  • nice job of sussing out whether a patient who's struggling with language actually has

  • a problem remembering and identifying words, or if they're just having a hard time processing

  • the information quickly.

  • But these tests should be regarded more skeptically when it comes to issues that are either way

  • more specific or way more broad.

  • Like, they won't be able to answer questions along the lines of, "Will Jesse get into Harvard?"

  • or "Are women smarter than men?"

  • They're just not designed to do that.

  • And in any case, simply knowing where you fall on a normal curve on a standardized test

  • doesn't mean much if the test is poorly designed, so along with being standardized, a good test

  • has high reliability, meaning it yields dependably consistent results.

  • One way to determine this is to have people take the same test a second time, or some

  • similar version of it.

  • If the two performances resemble one another -- if the scores correlate -- then the test

  • is thought to have good reliability.

  • And the third requirement for the testing trifecta is simply validity, or the extent

  • to which a test measures or predicts what it's supposed to.

  • And there are different kinds of validity -- for instance, if I take the WAIS IQ test

  • and my scores accurately predict how good my grades in college will be, that's a simple

  • kind of predictive or criterion validity.

  • On the other hand, if I take the test and my scores correlate strongly with my results

  • on another similar cognitive test, like the Stanford Binet, that falls under the broad

  • category of construct validity.

  • The key is that all of these are ways to see if a test measures what it claims to measure.

  • But the stickiest wicket of them all is what we make of the test scores themselves.

  • We've all heard plenty about the influence of both nature and nurture in psychology,

  • so the big question is: do our genetics influence our intelligence, or does our environment?

  • And this is an easy question to answer because they both do.

  • And that is important.

  • If the history of intelligence testing has taught us anything, it's that assuming everyone

  • is smart in the same way and for the same reason can lead to disastrously bad conclusions.

  • So let's look at the scientific evidence, and the best place for that is the wealth

  • of twin and adoption studies, which have been fascinatingly helpful in illustrating how

  • genetics and environment can both influence intelligence.

  • For example, research has shown that identical twins who were raised together have the highest

  • rate of similarity in intelligence scores of any group.

  • Fraternal twins who share only half the genes tend to be much less similar in their scores,

  • even when raised in the same home.

  • Likewise, neuroimaging studies show that certain brain regions, like those associated with

  • language, are structurally similar between identical twins, and show similar activity

  • while doing the same kinds of mental tasks.

  • The brains of fraternal twins raised in the same home are very similar in some areas,

  • but less so in others.

  • But identical twins who are raised together have the same brain, at least, according to

  • neuroimaging scans.

  • Some studies even showed that identical twins raised apart from each other show higher intelligence

  • correlation than fraternal twins raised together.

  • And maybe even more interesting is that these intelligence correlations actually increase

  • over time.

  • In one mega-study of eleven thousand twin pairs in four countries, that correlation

  • kept increasing from middle-childhood to adolescence to young adulthood and continued to increase

  • through adulthood.

  • Similar research has looked at adopted children and compared their scores with those of their

  • adopted siblings, parents, and biological parents.

  • And the results can be kind of surprising, because as adopted kids grow up, their mental

  • similarities to their adoptive families actually get smaller over time until there's virtually

  • no correlation by adulthood.

  • Instead, they become more similar in terms of mental aptitude to their biological parents

  • over time, even if they never met.

  • In other words: genes appear to matter.

  • You could take a hundred kids and raise them in the exact same way, and as adults, they'd

  • still have different aptitudes.

  • But, does this mean that when it comes to intelligence, we're all nature and no nurture?

  • Well, luckily, and somewhat obviously, no.

  • Life experiences and environment also matter.

  • One sad example of how early environments affect children can be found in the work of

  • American psychologist J. McVicker Hunt in a destitute Iranian orphanage in the 1970s.

  • Conditions were really, really bad; infants received minimal care, and whatever attention

  • they did get was on a routine schedule, never in response to whether they were cooing or

  • crying or anything else.

  • Basically, they were being raised with no cause and effect between their behaviors and

  • the responses of their caregivers, and as a result, they didn't learn how to communicate.

  • With no stimulation or social response, the kids were just kind of passive, vacant lumps.

  • Deprivation was essentially trumping any inborn intelligence.

  • So, Hunt started a program.

  • He trained caregivers to actually talk to infants, to teach them how to mimic sounds

  • and actions, and eventually, sounds and words from their language.

  • The results were tremendous.

  • The kids started to learn really quickly, and basically just came alive.

  • While it's an extreme example, Hunt's research showed how malleable early childhood intelligence

  • can be, especially in disadvantaged and stressful conditions.

  • So you can see that environment and heredity interact to affect intelligence, and that

  • some tricky implications can come out of that conclusion.

  • But that's hardly the only controversy when it comes to how we view and measure intelligence.

  • There have been some sensational headline-courting studies of genetic and social influences that

  • have suggested that fundamental differences in intelligence may exist between genders

  • and races, but many of these studies are tangled up in questions of how potential testing bias

  • may affect performance.

  • Basically, if a test inadvertently measures differences caused by cultural experiences

  • or social factors instead of what we might call "innate intelligence", then you might

  • say that the test is biased.

  • Extreme example: in the past, immigrants to the US were classified as "feeble minded"

  • if they couldn't answer distinctly American questions, like "Who was the first American

  • president?" or "What's a milkshake?".

  • Today, concerns about bias focuses on differences among members of the same general culture.

  • Say, a poor, rural kid who might be plenty smart, but will test low if questions involve

  • urban, upper-class concepts like taking taxis and drinking tea out of china cups or the

  • rules of tennis.

  • So the questions themselves can skew performance results, but who administers the test can

  • also affect outcomes.

  • Women tend to do better with a fellow female administrator, and African Americans often

  • score higher if their test is given by an African American instructor.

  • And the risk of bias may even fall to the test-takers' own expectations.

  • For example, many studies have found that if you give a math test to equally capable

  • men and women, but just before starting, you tell the subjects that women usually score

  • lower than men, you actually negatively affect the women's performance.

  • This self-fulfilling concern that you might mess up and inadvertently fulfill some negative

  • stereotype is called stereotype threat.

  • It was first described by social psychologist Claude Steele and Joshua Aronson, and it's

  • been demonstrated frequently across a whole host of interesting studies.

  • Now, we've only scratched the surface of this mess that is intelligence testing.

  • An important thing to remember next time you ace or bomb a test is that you are far more

  • complicated and nuanced than any test score.

  • Don't let a number puff you up or drag you down, and don't let it define you.

  • We all have room for self-improvement.

  • We are all full of infinite surprising potential.

  • Ah, and answers to the questions I asked earlier: A piano is a musical instrument played using

  • a keyboard, banana is the least similar to the others, juice is to class as hand is to

  • glove, the number two does not belong in the series, and Bernice began with twenty-three

  • jellybeans.

  • Today, your intelligent mind learned how we currently use WAIS and WISC tests to measure

  • intelligence, and how important it is that a test be standardized, reliable, and valid.

  • We also looked at how genetics, environment, testing bias, and stereotype threat can affect

  • IQ test performance.

  • Thank you for watching, especially to all of our Subbable subscribers who make Crash

  • Course possible.

  • To find out how you can become a supporter, just go to Subbable.com/CrashCourse.

  • This episode was written by Kathleen Yale, edited by Blake de Pastino, and our consultant

  • is Dr. Ranjit Bhagwat.

  • Our director and editor is Nicholas Jenkins, the script supervisor is Michael Aranda, who

  • is also our sound designer, and the graphics team is Thought Café.

In your lifetime, you have probably stared down any number of ability tests and course

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