IQ: What it is, and what it isn't

[Eris]

The inspiration for this is a locked thread that can be found here. In particular, the snide comment by Gullible Jones slamming IQ as a form of intelligence test. ("Because we all know that IQ is an accurate measure of intellectual ability... right, everyone?") Now, I know the post is old, but it's representative of a entire line of thought that annoys the hell out of me, so I'm going to take the opportunity to pontificate for a minute, and maybe someone will actually learn something.

My primary source for this rant is, for the record, Life-Span Human Development, Fifth Edition, by Carol Sigelman and Elizabeth Rider. Although a general college-level textbook on human development from cradle to grave, about a third of it is devoted to intelligence and other cognitive functions, and it's up to date with all the research further cited if anyone wants to know where I'm pulling all this from.

Starting at the beginning, IQ is a relative measure of certain elements of cognitive ability. Its scoring is scaled such that 100 is always the mean and 15 is always the standard deviation. So, ~67% of the members of a population have IQs of 85 - 115, ~95% range from 70 - 130, and 99.7% fall between 55 - 145. In most populations this gives a lovely bell curve, and the actual numbers are therefore pretty meaningless. They're just numerical designations used as labels so we can gauge relative performance on the tests.

IQ tests for a very limited and well defined set of criteria. The original IQ tests were set up by Alfred Binet and Theodore Simon at the behest of the French government in 1904 to test for "dull" children who might need special attention. They created a battery of tests aimed at measuring skills they believed to be necessary for classroom learning: attention, perception, memory, reasoning, verbal comprehension, etcetera. If IQ tests seem like they aim at testing knowledge as well as "intelligence", that's completely right, since they're designed at their heart to identify children who are struggling in school. The scale Binet devised was refined by Lewis Terman and translated into English for use with American children, and it became known as the Stanford-Binet Intelligence Scale (Terman worked at Stanford). It explicitly goes after children, since the result categorises by comparing mental age to physiological age, and it splits up results by cohort. A score of 100 therefore means that the person is average amongst their age group. And further, you can track and change IQ dependent on age - it's legitimate under this (out of date version of the) scale to say someone is 10 years old, but is mentally an average five year old. Stanford-Binet is still in use, but now in its (if I recall correctly) fifth edition, so it's being updated and refined. For instance, we've dropped the notion of mental age, and simply compare you to others in your age group.

I say all this because it's important to remember that IQ tests don't exist in a vacuum. They may not test for every kind of intelligence or cognitive ability, but they aren't supposed to. They're a tool to help researchers and educators identify and help people who are struggling in an academic environment. It does apply more broadly to that, as we'll see in a moment, but that's its purpose, and its form is explicitly tied to that.

What does IQ test for? Well, much of the same stuff it did back over a hundred years ago. The real tests, rather than the dinky online "Test Your IQ Fast!" things you see advertised, are quite long and quite thorough. One major one used, the Weschsler Preschool and Primary Scale, has a few versions aimed at people ages 3 - 8, 6 - 16, adults, and so on. They yield scores for verbal IQ, based on things like vocabulary, general knowledge, arithmetic reasoning, and so on, and a performance IQ, based on nonverbal skills like puzzles, mazes, geometric matching, and picture rearrangement to form coherent stories. There are other tests as well, and still considerable research going into the subject - new methods like dynamic assessment (tests that evaluate how aptly a child learns new material after presented with competent instruction) are broadening what IQ tests can measure.

So, that's what an IQ test is and why it's set up that way, so how much does it work? Well, we have to break that up by age. Infants for obvious reasons can't be tested, since all IQ tests have strong verbal components, so we start with children. (Infants do have a thing called DQ - developmental quotient - which but that's a completely different thing, that's not strongly correlated with IQ.)

Children's IQ scores (basically people ages around 4 - 12 or so) start out highly volatile. The average change in a child's scores is 28.5 points, a third change more than 30 points, and changes of up to 74 points have been recorded. Around the age of seven, however, the score stabilises, and the score at seven is clearly related with the score at age 12. There is active debate over the factors which cause this volatility. Some of it appears to be random, but we still have some leads. Unstable home environments leads to more volatility, for instance. Parents play a role too, and those who strike a balance between strictness and flexibility foster more IQ growth, while impoverished environments inhibit it. (Both effects are cumulative, too.)

When a child matures into an adolescent (varies as to exactly when, but often between 10 and 13), there's a huge spurt of brain development, and this is where we start gathering all sorts of useful information out of IQ. After all, the tests were originally designed just for this. And they work, too. There is a correlation of +0.50 between IQ scores and grades for both children and adolescents, which is mind-bogglingly high. IQ is one of the best predictors of academic success we have. It also is correlated at +0.55 with number of years of education attained - people with high IQs are much much less likely to drop out, and more likely to go on to college. IQ is better at predicting HS grades than college grades, but the reasons are too complex to go into right here, and aren't entirely non-contraversial anyhow. This is an open field of research.

On to adulthood. I'll touch on only two things here: occupational success and health. There is a strong correlation between IQ and success in the workplace, again one of the best we have. It varies from +0.3 and +0.5 on average, depending on what you're testing for (supervisor ratings, economic success, etc) and who you're testing, as the correlations vary by factors such as race (blacks have a stronger correlation between their IQs and their success than whites for instance). Part of this is a no brainer: a lot of high prestige and high paying jobs like lawyers and doctors require some native intellectual capacity that farm hand does not. But even then, the higher your IQ, the higher you'll tend to rise, even within elite professions. This correlation holds right down to the level of weekly income: you literally will make more on average the higher your IQ is.

Finally, people who score higher on IQ tests tend to live longer and be healthier than those who score lower. There was a great study done on the people born in 1921, since almost all of them took a standard intelligence test in 1932 when they were 11. There was a follow up using health and death records decades later and it was found that those who had scored one standard deviation lower (15 pts remember) were less likely to be alive at the age of 76, and more likely to have gone through cancers, cardiovascular disease, have diabetes, and so on. Again, this isn't too surprising - IQ is correlated with socioeconomic status, which is correlated with health and life expectancy. Further, people with high IQs may be more adept at realising the importance of preemptive care, and be better at managing conditions like diabetes when they do get them, leading to general better health, and consequently lengthened life spans. Basically, smart people tend to be better at learning about their health, and have the resources to do something about it as well, but the correlations between heath and IQ is still a very active field of research, so take that with a grain of salt.

So yes, IQ is not the end all be all of intelligence. It totally misses, for instance, bodily-kinaesthetic intelligence amongst other things, and like all tests for intelligence it is by its nature somewhat fuzzy, as it's trying to give a numerical value to something not inherently numeric. But it still remains one of the most powerful, if not the most powerful tool at our disposal in predicting success in school and in careers, so it is far from deserving this pooh-poohing either. IQ is not perfect, but within its context, it's one of the best measures of intelligence we have.

[Stark]

It continues to be ironic that everyone I know who has tested well on a clinical IQ test believes them to be complete rubbish for determining what most people think they determine.

[loomer]

Well, they aren't perfect, that's certain. I score relatively highly, at about 130. But the thing is, I've never been very good at mathematics which do tend to be a fairly large component of IQ tests. So while that's fantastic as a teaching thing, since it would've let teachers know that 'hey, he could probably use a tutor', it's not so great as a measure of actual intelligence. Mine lies in the creative fields rather than the logical - with the nice effect of being harder to quantify.

Although ironically, I've noted that the correlations between higher IQs and higher socio-economic status do not apply within my community. Back at school, a full three quarters of the gifted class were lower class and from broken homes rather than middle or upper class. In cities, however, this changes - with less people with naturally high abilities and more rich people with tutors influencing the bell curve.

[Boyish-Tigerlilly]

In education, IQ tests are valuable because they tend to correlate highly with academic success, given instruction and effort. The modern exams are quite a bit more reliable, better than the old ones, because much of the bias has been specifically targeted, whereas before, not so much.

They shouldn't be used as a single measure for making important decisions, despite their utility, or for setting standards on new students before they do anything. IN the past, when teachers knew the IQ scores of their students, it created self-fulfilling prophecies as they lowered their standards and expectations for the students with lower IQ.

They need to train themselves, if it do know, to look at multiple assessments or use the IQ to pinpoint potential weaknesses for additional help. But for that, a Diagnostic Aptitude Test might be more useful.

[dragon]

IQ tests can be deceptive take me for exmple my official IQ is 130 yet I suck at many things people whom lower scores do better. For example I suck at spelling an language skills but I am fairly decent with abstract sciences as long as you don't get into the nit and gritty of the subject.

My one area I am really good at is computer but I don't like them so I haven't learned as much as I should have

My wife whom has a 140, I belive, speaks 5 languages fluently, is almost finished with her Ph'd in German Literature, yet don't even try basic math and science with her as she will be completly lost despite mutiple classes in the subjects.

So I would say IQ is deffinitely not what many make it out to.

[Zac Naloen]

My understanding of IQ tests is that they are an indicator of potential, but not necessarily the be all and end all.

A persons personality will also affect how hard they work at something as well, How much effort you put in can be just as important as how easily you understand it.

[Rye]

My understanding was more intellectual aptitude in various fields as noted in the OP, then for whatever reason, those different aspects are boiled down into an average score. I can't say I'm fully convinced by that final part; I mean, it seems much less immediately useful than the constituent scores.

That said, it is pretty good at predicting the crowd of people you'll be best able to converse with, for instance, even if it does say some uncomfortable things about racial trends.

[Eris]

As Zuul pointed out, it is perfectly possible for people to have a high IQ and still suck at some mental tasks, or someone with a low IQ to do something really well, since IQ scores are an average, and moreover an average of a limited and well-defined set of tasks. There are other forms of intelligence not tested on IQ tests as well. I mentioned bodily-kinaesthetic intelligence - loosely the ability to use your body well in a coordinated and complex way, at things like athletics or many crafts. Likewise certain capabilities useful in interpersonal relations, like empathy and kinds of non-logical inference, none of these are tested for in an IQ test. But then, anyone who knows what an IQ test does would never claim it's the end all be all.

@Stark: I'm always struck by that kind of thing too, although I'm not sure if it's more just a general disdain propagated by it being trendy, a streak of populism, or what. No one has yet found a better predictor for school performance and SES than IQ, but it's still very popular to disparage it as not a real indicator of intelligence. (Although on a tangent, intelligence itself is one of those weasel words that can mean almost whatever you want it to, so I wonder if most of them aren't just playing semantic games.)

[Stark]

People who are smart can generally see that whatever success they have is actually due to the work they put in, or that their laziness gives them a less successful life than 'less smart' people with more dedication. It's stupid people who think 'lololol I have teh IQz I is smrtr than u!!!!'

In general, when I'm talking of 'intelligence' I'm referring to what would be better termed 'abstract reasoning' or 'learning potential'; the ability to do new things or implement new learnings. Again, it's stupid people who think 'being smart' = 'magically know things'.

[CaptainZoidberg]

This picture explains the concept of IQ (or more precisely the general intelligence factor pretty well):



IQ is just the overlap between important mental abilities. Of course someone with a higher IQ is more likely to have better ability at XYZ then someone with a lower IQ, but that isn't necessarily the case.