{"id":129,"date":"2003-11-17T21:47:11","date_gmt":"2003-11-18T02:47:11","guid":{"rendered":"\/?p=129"},"modified":"2003-11-17T21:47:11","modified_gmt":"2003-11-18T02:47:11","slug":"what-good-is-iq","status":"publish","type":"post","link":"http:\/\/esr.ibiblio.org\/?p=129","title":{"rendered":"What good is IQ?"},"content":{"rendered":"<p>A reader asks:<\/p>\n<blockquote>\n<p>To clarify, while I believe natural selection explains a lot I have<br \/>\ncaveats about IQ as a tool for testing intelligence. If you can&#8217;t<br \/>\nmeasure the coast of France with a single number how can you do it<br \/>\nwith human intelligence?<\/p>\n<\/blockquote>\n<p>Easily.  Human intelligence is a great deal less complex than the<br \/>\ncoast of France. :-)<\/p>\n<p>It&#8217;s fashionable nowadays to believe that intelligence is some<br \/>\ncomplicated multifactor thing that can&#8217;t be captured in one number.<br \/>\nHowever, one of the best-established facts in psychometry (the science<br \/>\nof measuring mind) is that it is quite difficult to write a test of<br \/>\nmental ability that is not at least 50% correlated with all other such<br \/>\ntests.  Or, to put it another way, no matter how you design ten tests for<br \/>\nmental ability, at least about half the variance in the scores for any one<br \/>\nof them statistically appears to be due to a &#8220;general intelligence&#8221;<br \/>\nthat shows up on the other nine tests as well.<\/p>\n<p>Psychometricians call this general intelligence measure &#8220;g&#8221;.  It<br \/>\nturns out to predict important real-world success measures quite well<br \/>\n&mdash; not just performance in school but income and job success as<br \/>\nwell.  The fundamental weakness in multiple-factor theories of intelligence<br \/>\nis that measures of intelligence <em>other<\/em> than g appear to predict<br \/>\nvery little about real-world outcomes.  So you can call a lot of other<br \/>\nthings &#8220;intelligence&#8221; if you want to make people feel warm and fuzzy,<br \/>\nbut doing so simply isn&#8217;t very useful in the real world.<\/p>\n<p>Some multifactor theorists, for example, like to describe accurate<br \/>\nproprioception (an acute sense of body position and balance) as a kind<br \/>\nof intelligence.  Let&#8217;s say we call this &#8220;p&#8221;.  The trouble with this<br \/>\nis that there are very few situations in which a combination of high p<br \/>\nand low g is actually useful &mdash; people need to be able to balance<br \/>\ncheckbooks more often than they need to walk high wires.  Furthermore,<br \/>\ng is easier to substitute for p than the other way around; a person<br \/>\nwith high g but low p can think up a way to not have to walk a high<br \/>\nwire far better than a person with low g but high p can think up a way<br \/>\nnot to have to balance a checkbook. So g is in a strict functional<br \/>\nsense more powerful than p. Similar arguments apply to most of the<br \/>\nother kinds of specialized non-g &#8216;intelligence&#8217; that have been<br \/>\nproposed.<\/p>\n<p>Once you know about g, you can rank mental-capability tests by<br \/>\nhow well their score correlates with g.  IQ is valuable because a<br \/>\nwell-composed IQ test measures g quite effectively.  For purposes<br \/>\nof non-technical discussion, g and IQ can be considered the same, and<br \/>\npychometricians now accept that an IQ test which does not closely track<br \/>\ng is defective.<\/p>\n<p>A lot of ink has been spent by people who aren&#8217;t psychometricians<br \/>\non insisting that g is a meaningless statistical artifact.  The most<br \/>\nfamous polemic on this topic was Stephen Jay Gould&#8217;s 1981 book<br \/>\n<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 \/>\nwrong<\/a>, and in some respects rather dishonest.  Gould was a<br \/>\nbelieving Marxist; his detestation of g was part of what he perceived<br \/>\nas a vitally important left-versus right <em>kulturkampf<\/em>.  It is<br \/>\nvery unfortunate that he was such a persuasive writer.<\/p>\n<p>Unfortunately for Gould, g is no statistical phantom.  Recently g<br \/>\nand IQ have been shown to correlate with measurable physiological<br \/>\nvariables such as the level of trace zinc in your hair and performance<br \/>\non various sorts of reaction-time tests.  There are hints in the<br \/>\nrecent literature that g may be largely a measure of the default level<br \/>\nof a particular neurotransmitter associated with states of mental<br \/>\nalertness and speed of thought; it appears that calling people of<br \/>\nsubnormal intelligence &#8220;slow&#8221; may not be just a metaphor!<\/p>\n<p>IQ is one of several large science-related issues on which<br \/>\npolitical bias in the dominant media culture has lead it to present as<br \/>\nfact a distorted or even reversed version of the actual science.  In<br \/>\n1994, after Murray and Herrnstein&#8217;s <cite>The Bell Curve<\/cite> got a<br \/>\nthoroughly undeserved trashing, fifty leading psychometricians and<br \/>\npsychologists co-signed a summary of <a href='http:\/\/www.mugu.com\/cgi-bin\/Upstream\/Issues\/bell-curve\/support-bell-curve.html'>mainstream<br \/>\nscience on intelligence<\/a>.  It makes eye-opening reading.<\/p>\n<p>The reasons many popular and journalistic accounts continue to<br \/>\ninsist that IQ testing is at best meaningless and at worst a sinister<br \/>\nplot are twofold.  First, this belief flatters half of the population.<br \/>\n&#8220;My IQ may be below average, but that doesn&#8217;t matter because IQ is<br \/>\nmeaningless and I have high emotional intelligence!&#8221; is,<br \/>\nunderstandably, a favorite evasion maneuver among dimwits.  But that<br \/>\nisn&#8217;t the worst of it.  The <em>real<\/em> dynamite is not in<br \/>\nindividual differences but rather that the distribution of IQ (and<br \/>\nhence of g) varies considerably across groups in ways that are<br \/>\npolitically explosive.<\/p>\n<p>Men vs. women is the least of it.  With other variables controlled,<br \/>\nmen and women in a population have the same mean IQ, but the<br \/>\ndispersion differs.  The female bell curve is slightly narrower, so<br \/>\nwomen have fewer idiots and fewer geniuses among them.  Where this<br \/>\ngets touchy is that it may do a better job than cultural sexism of<br \/>\nexplaining why most of the highest achievers in most fields are male<br \/>\nrather than female. Equal opportunity does not guarantee equal<br \/>\nresults, and lot of feminist theory goes out the window.<\/p>\n<p>But male\/female differences are insignificant compared to the real<br \/>\nhot potato: differences in the mean IQ of racial and ethnic groups.<br \/>\nThese differences are real and they are large enough to have severe<br \/>\nimpact in the real world.  In previous blog entries I&#8217;ve mentioned the<br \/>\none-standard-deviation advantage of Ashkenazic Jews over gentile<br \/>\nwhites; that&#8217;s roughly fifteen points of IQ.  Pacific-rim Asians<br \/>\n(Chinese, Japanese, Koreans etc.) are also brighter on average by a<br \/>\ncomparable margin.  So, oddly enough, are ethnic Scots &mdash; though<br \/>\nnot their close kin the Irish.  Go figure&#8230;<\/p>\n<p>And the part that, if you are a decent human being and not a racist<br \/>\nbigot, you have been dreading: American blacks average a standard<br \/>\ndeviation <em>lower<\/em> in IQ than American whites at about 85.  And<br \/>\nit gets worse: the average IQ of <em>African<\/em> blacks is lower<br \/>\nstill, not far above what is considered the threshold of mental<br \/>\nretardation in the U.S.  And yes, it&#8217;s genetic; g seems to be about<br \/>\n85% heritable, and recent studies of effects like regression towards<br \/>\nthe mean suggest strongly that most of the heritability is DNA rather<br \/>\nthan nurturance effects.<\/p>\n<p>For anyone who believe that racial equality is an important goal,<br \/>\nthis is absolutely horrible news.  Which is why a lot of<br \/>\nwell-intentioned people refuse to look at these facts, and will<br \/>\nattempt to shout down anyone who speaks them in public.  There have<br \/>\nbeen several occasions on which leading psychometricians have had<br \/>\ntheir books canceled or withdrawn by publishers who found the actual<br \/>\nscientific evidence about IQ so appalling that they refused to print<br \/>\nit.<\/p>\n<p>Unfortunately, denial of the facts doesn&#8217;t make them go away.  Far from<br \/>\nbeing meaningless, IQ may be the single most important statistic about<br \/>\nhuman beings, in the precise sense that differences in g probably drive<br \/>\nindividual and social outcomes more than any other single measurable<br \/>\nattribute of human beings.<\/p>\n<p>Mean IQ differences do not justify making assumptions about any individual.<br \/>\nThere are African black geniuses and Ashkenazic Jewish morons; humanity and<br \/>\nethics demand that we meet each individual human being as an individual,<br \/>\nwithout prejudice.  At the same time, group differences have a significance<br \/>\ntoo great to ignore.  In the U.S., blacks are 12% of the population but<br \/>\ncommit 50% of violent crimes; can anyone honestly think this is<br \/>\nunconnected to the fact that they average 15 points of IQ lower than the<br \/>\ngeneral population?  That stupid people are more violent is a fact<br \/>\nindependent of skin color.<\/p>\n<p>And that is actually a valuable hint about how to get beyond<br \/>\nracism.  A black man with an IQ of 85 and a white man with an IQ of 85<br \/>\nare about equally likely to have the character traits of poor impulse<br \/>\ncontrol and violent behavior associated with criminality &mdash; and<br \/>\nboth are far more likely to have them than a white or black man with<br \/>\nan IQ of 110.  If we could stop being afraid of IQ and face up to it,<br \/>\nthat would give us an objective standard that would banish racism per<br \/>\nse.  IQ matters so much more than skin color that if we started paying<br \/>\nserious attention to the former, we might be able to stop paying<br \/>\nattention to the latter.<\/p>\n<p>UPDATE: An excellent summary of science relating to g<br \/>\nis <a href='http:\/\/psycprints.ecs.soton.ac.uk\/archive\/00000658\/'>here<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>A reader asks: To clarify, while I believe natural selection explains a lot I have caveats about IQ as a tool for testing intelligence. If you can&#8217;t measure the coast of France with a single number how can you do it with human intelligence? Easily. Human intelligence is a great deal less complex than the&hellip; <a class=\"more-link\" href=\"http:\/\/esr.ibiblio.org\/?p=129\">Continue reading <span class=\"screen-reader-text\">What good is IQ?<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[11],"tags":[],"class_list":["post-129","post","type-post","status-publish","format-standard","hentry","category-science","entry"],"_links":{"self":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/posts\/129","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=129"}],"version-history":[{"count":0,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=\/wp\/v2\/posts\/129\/revisions"}],"wp:attachment":[{"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=129"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=129"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/esr.ibiblio.org\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=129"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}