140 lines
9.6 KiB
Plaintext
140 lines
9.6 KiB
Plaintext
What good is IQ?
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<p>A reader asks:</p>
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<blockquote>
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<p>To clarify, while I believe natural selection explains a lot I have<br />
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caveats about IQ as a tool for testing intelligence. If you can’t<br />
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measure the coast of France with a single number how can you do it<br />
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with human intelligence?</p>
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</blockquote>
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<p>Easily. Human intelligence is a great deal less complex than the<br />
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coast of France. :-)</p>
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<p>It’s fashionable nowadays to believe that intelligence is some<br />
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complicated multifactor thing that can’t be captured in one number.<br />
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However, one of the best-established facts in psychometry (the science<br />
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of measuring mind) is that it is quite difficult to write a test of<br />
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mental ability that is not at least 50% correlated with all other such<br />
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tests. Or, to put it another way, no matter how you design ten tests for<br />
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mental ability, at least about half the variance in the scores for any one<br />
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of them statistically appears to be due to a “general intelligence”<br />
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that shows up on the other nine tests as well.</p>
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<p>Psychometricians call this general intelligence measure “g”. It<br />
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turns out to predict important real-world success measures quite well<br />
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— not just performance in school but income and job success as<br />
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well. The fundamental weakness in multiple-factor theories of intelligence<br />
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is that measures of intelligence <em>other</em> than g appear to predict<br />
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very little about real-world outcomes. So you can call a lot of other<br />
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things “intelligence” if you want to make people feel warm and fuzzy,<br />
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but doing so simply isn’t very useful in the real world.</p>
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<p>Some multifactor theorists, for example, like to describe accurate<br />
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proprioception (an acute sense of body position and balance) as a kind<br />
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of intelligence. Let’s say we call this “p”. The trouble with this<br />
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is that there are very few situations in which a combination of high p<br />
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and low g is actually useful — people need to be able to balance<br />
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checkbooks more often than they need to walk high wires. Furthermore,<br />
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g is easier to substitute for p than the other way around; a person<br />
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with high g but low p can think up a way to not have to walk a high<br />
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wire far better than a person with low g but high p can think up a way<br />
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not to have to balance a checkbook. So g is in a strict functional<br />
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sense more powerful than p. Similar arguments apply to most of the<br />
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other kinds of specialized non-g ‘intelligence’ that have been<br />
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proposed.</p>
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<p>Once you know about g, you can rank mental-capability tests by<br />
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how well their score correlates with g. IQ is valuable because a<br />
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well-composed IQ test measures g quite effectively. For purposes<br />
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of non-technical discussion, g and IQ can be considered the same, and<br />
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pychometricians now accept that an IQ test which does not closely track<br />
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g is defective.</p>
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<p>A lot of ink has been spent by people who aren’t psychometricians<br />
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on insisting that g is a meaningless statistical artifact. The most<br />
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famous polemic on this topic was Stephen Jay Gould’s 1981 book<br />
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<cite>The Mismeasure of Man</cite>, a book which was <a href='http://www.mugu.com/cgi-bin/Upstream/Issues/psychology/IQ/carroll-gould.html'>muddled,<br />
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wrong</a>, and in some respects rather dishonest. Gould was a<br />
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believing Marxist; his detestation of g was part of what he perceived<br />
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as a vitally important left-versus right <em>kulturkampf</em>. It is<br />
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very unfortunate that he was such a persuasive writer.</p>
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<p>Unfortunately for Gould, g is no statistical phantom. Recently g<br />
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and IQ have been shown to correlate with measurable physiological<br />
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variables such as the level of trace zinc in your hair and performance<br />
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on various sorts of reaction-time tests. There are hints in the<br />
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recent literature that g may be largely a measure of the default level<br />
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of a particular neurotransmitter associated with states of mental<br />
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alertness and speed of thought; it appears that calling people of<br />
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subnormal intelligence “slow” may not be just a metaphor!</p>
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<p>IQ is one of several large science-related issues on which<br />
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political bias in the dominant media culture has lead it to present as<br />
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fact a distorted or even reversed version of the actual science. In<br />
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1994, after Murray and Herrnstein’s <cite>The Bell Curve</cite> got a<br />
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thoroughly undeserved trashing, fifty leading psychometricians and<br />
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psychologists co-signed a summary of <a href='http://www.mugu.com/cgi-bin/Upstream/Issues/bell-curve/support-bell-curve.html'>mainstream<br />
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science on intelligence</a>. It makes eye-opening reading.</p>
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<p>The reasons many popular and journalistic accounts continue to<br />
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insist that IQ testing is at best meaningless and at worst a sinister<br />
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plot are twofold. First, this belief flatters half of the population.<br />
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“My IQ may be below average, but that doesn’t matter because IQ is<br />
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meaningless and I have high emotional intelligence!” is,<br />
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understandably, a favorite evasion maneuver among dimwits. But that<br />
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isn’t the worst of it. The <em>real</em> dynamite is not in<br />
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individual differences but rather that the distribution of IQ (and<br />
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hence of g) varies considerably across groups in ways that are<br />
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politically explosive.</p>
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<p>Men vs. women is the least of it. With other variables controlled,<br />
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men and women in a population have the same mean IQ, but the<br />
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dispersion differs. The female bell curve is slightly narrower, so<br />
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women have fewer idiots and fewer geniuses among them. Where this<br />
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gets touchy is that it may do a better job than cultural sexism of<br />
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explaining why most of the highest achievers in most fields are male<br />
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rather than female. Equal opportunity does not guarantee equal<br />
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results, and lot of feminist theory goes out the window.</p>
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<p>But male/female differences are insignificant compared to the real<br />
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hot potato: differences in the mean IQ of racial and ethnic groups.<br />
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These differences are real and they are large enough to have severe<br />
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impact in the real world. In previous blog entries I’ve mentioned the<br />
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one-standard-deviation advantage of Ashkenazic Jews over gentile<br />
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whites; that’s roughly fifteen points of IQ. Pacific-rim Asians<br />
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(Chinese, Japanese, Koreans etc.) are also brighter on average by a<br />
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comparable margin. So, oddly enough, are ethnic Scots — though<br />
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not their close kin the Irish. Go figure…</p>
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<p>And the part that, if you are a decent human being and not a racist<br />
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bigot, you have been dreading: American blacks average a standard<br />
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deviation <em>lower</em> in IQ than American whites at about 85. And<br />
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it gets worse: the average IQ of <em>African</em> blacks is lower<br />
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still, not far above what is considered the threshold of mental<br />
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retardation in the U.S. And yes, it’s genetic; g seems to be about<br />
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85% heritable, and recent studies of effects like regression towards<br />
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the mean suggest strongly that most of the heritability is DNA rather<br />
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than nurturance effects.</p>
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<p>For anyone who believe that racial equality is an important goal,<br />
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this is absolutely horrible news. Which is why a lot of<br />
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well-intentioned people refuse to look at these facts, and will<br />
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attempt to shout down anyone who speaks them in public. There have<br />
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been several occasions on which leading psychometricians have had<br />
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their books canceled or withdrawn by publishers who found the actual<br />
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scientific evidence about IQ so appalling that they refused to print<br />
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it.</p>
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<p>Unfortunately, denial of the facts doesn’t make them go away. Far from<br />
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being meaningless, IQ may be the single most important statistic about<br />
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human beings, in the precise sense that differences in g probably drive<br />
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individual and social outcomes more than any other single measurable<br />
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attribute of human beings.</p>
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<p>Mean IQ differences do not justify making assumptions about any individual.<br />
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There are African black geniuses and Ashkenazic Jewish morons; humanity and<br />
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ethics demand that we meet each individual human being as an individual,<br />
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without prejudice. At the same time, group differences have a significance<br />
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too great to ignore. In the U.S., blacks are 12% of the population but<br />
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commit 50% of violent crimes; can anyone honestly think this is<br />
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unconnected to the fact that they average 15 points of IQ lower than the<br />
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general population? That stupid people are more violent is a fact<br />
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independent of skin color.</p>
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<p>And that is actually a valuable hint about how to get beyond<br />
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racism. A black man with an IQ of 85 and a white man with an IQ of 85<br />
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are about equally likely to have the character traits of poor impulse<br />
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control and violent behavior associated with criminality — and<br />
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both are far more likely to have them than a white or black man with<br />
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an IQ of 110. If we could stop being afraid of IQ and face up to it,<br />
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that would give us an objective standard that would banish racism per<br />
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se. IQ matters so much more than skin color that if we started paying<br />
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serious attention to the former, we might be able to stop paying<br />
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attention to the latter.</p>
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<p>UPDATE: An excellent summary of science relating to g<br />
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is <a href='http://psycprints.ecs.soton.ac.uk/archive/00000658/'>here</a></p>
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