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Can Human Intelligence be Measured by Artificial Tests?
(this is a follow up to Bush Supporters Dumber than Kerry Supporters?)

In short, the answer is yes. For a variety of reasons, including (perhaps most prominently) the unsavory fact that a variety of minority groups tend to have lower scores on average on IQ tests, many people don't like this idea. But the fact of the matter is that there is little doubt within the scientific/psychological community that intelligence (preferably referred to as general cognitive ability, or g, to avoid the controversy that comes with the "intelligence" label) is measurable in humans, and further, that IQ tests are a reasonable indicator of that measure.

Here are some relevant quotes from a widely used book on behavioral genetics (Behavioral Genetics - Robert Plomin, John C. DeFries, Gerald E. McClearn, and Peter McGuffin):

General cognitive ability is one of the most well studied domains in behavioral genetics. Nearly all this genetic research is based on a model, called the psychometric model. According to this model, cognitive abilities are organized heirarchically (Carroll, 1993, 1997), from specific tests to broad factors to general cognitive ability...

These broad factors intercorrelate modestly. That is, in general, people who do well on tests of verbal ability tend to do well on tests of spatial ability. g, that which is in common among these broad factors, was discovered by Charles Spearman over 90 years ago...

Most people are familiar with intelligence tests, often called IQ tests (intelligence quotient tests). These tests typically assess several cognitive abilities and yield total scores that are reasonable indices of g...

Despite the massive data pointing to g, considerable controversy continues to surround g and IQ tests, especially in the media. There is a wide gap between what lay people (including scientists in other fields) believe and what experts believe. Most notably, lay people often hear in the popular press that the assessment of intelligence is circular--intelligence is what intelligence tests assess. To the contrary, g is one of the most reliable and valid measures in the behavioral domain. Its long-term stability after childhood is greater than the stability of any other behavioral trait. And it predicts important social outcomes such as education and occupational levels far better than any other trait (Gottfredson, 1997)... (pages 156-158)



Of course, I'm certainly not one to claim that the mere fact that experts agree means that they must be right. Particular intelligence tests, and to a lesser extend the idea of intelligence testing and general cognitive ability, are all open to criticism.

But the kind of criticism they are open to is not the knee-jerk reactions of armchair "psychologists" who get angry at the thought of intelligence being something that can be measured. This isn't the sort of thing that will simply cease to be the case because we don't like it, because it doesn't seem politically correct.

The heated reaction to The Bell Curve, a book putting forward the claim that certain ethnic groups have a lower average intelligence than other groups, demonstrates this clearly. I'm not overly familiar with this book or its claims - for all I know, it might well be deeply flawed and incorrect in its assertions. A great many people believe this to be the case. Unfortunately, this belief is not motivated by any understanding of the book or of the subject it addresses; they believe the book must be false because it is simply unacceptable to say that certain ethnic groups have lower average intelligences than other groups (even if, as I recall, the differences aren't really that much).

Some people seem to think that such a claim is racist, though it is worth nothing that Caucasians did not have the highest average intelligence according to The Bell Curve's data - Asians did. This feeling is understandable, as in the past there has been a fair amount of questionable "science" used to fuel ideologies of racial superiority. I can't say whether or not this was the case in this particular book, though nothing I've seen has given me any reason to believe that the research was at all motivated by racism.

At some point, we need to gather ourselves and become willing to accept the possibility that such a claim might be true, even if we don't like it. IQ really does provide a reasonable measure of a real measurable trait, general cognitive ability - and it is possible that we will find that some groups have, on average, a higher general cognitive ability than others.

We will never know whether or not such claims are really true if we are already bent on having the answer come out our way. With such a mindset, no matter how much evidence we have, we will find something to discredit it by (even if we must do so illegitimately) if it doesn't come out the right way. And we will embrace any findings that fit the outcome we prefer, even if the science behind it is deeply flawed. This is the mindset that previously allowed bad "science" to confer legitimacy on ideas of racial superiority, and we should rid ourselves of it.

Closing Thoughts

I don't think the idea of people having a measurable intelligence is that hard to swallow. It certainly isn't counter-intuitive - most everyone recognizes that some people are much smarter, and others much dumber, than others. And these smarter people just happen to be the ones who tend to score well on intelligence tests (as well as on tests like the SAT that are reasonably correlated with IQ scores), and the less intelligent ones happen to be the same ones who score poorly.

If the labels offend, you can always change them (thats why psychologists use g instead of "intelligence"). This might take some of the bite out of unpleasant results, but the meaning doesn't change.

Intelligence is also something that doesn't change much - that is, common environment doesn't have a whole lot to do with it. Many people think that people of low intelligence have low intelligence because they came from bad homes and bad school systems. But scientific study simply hasn't supported this - not exactly, anyway.

There have been adoption studies in which low-IQ children (around 85-90 on average) were adopted into homes of families whose biological children had reasonably high IQs (usually between 115-125 on average). And, for a time, these adoptees generally did show a 5-10 point increase in scores on IQ tests. They didn't come up to the levels of the biological children, but the scores did show significant improvement.

But the most notable result of this study is that after these adopted children grew up and/or left the home, their performance on IQ tests fell back down to right around what it had been before. Even among children who were adopted when they were very young, a growing up in a home with intelligent parents/siblings and attending good schools did not cause any permanent increase in IQ test. They got the boost while they were in that environment, but the effect ended when they were no longer in it.

These tests suggest that an environment conducive to learning helps individuals express more of their intellectual potential, but it does not raise actual intelligence.

What do YOU think?
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