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Posner: "IQ is understood to reflect both genetic endowment and environmental factors, particularly factors operative very early in a child’s life, including prenatal care, maternal health, the educational level of the parents, family stability, and poverty (all these are correlated, and could of course reflect low IQs of parents as well as causing low IQs in their children). The case for very early intervention in children’s development ... can be understood as an effort to lift IQs in the black and Hispanic communities and by doing so improve the educational performance of black and Hispanic children.."

But that experiment - enriching the environment for minority youth - is in effect already taking place in the homes of children of affluent minority parents. So in such children we should see a reduction of the performance gap when their test scores (eg on the SAT) are compared to whites with similar backgrounds. But..

...there is a major flaw in the thesis that income differences explain the racial gap. Consider these observable facts from The College Board’s 2006 data on the SAT:

. Whites from families with incomes of less than $10,000 had a mean SAT score of 993. This is 130 points higher than the national mean for all blacks.
. Whites from families with incomes below $10,000 had a mean SAT test score that was 17 points higher than blacks whose families had incomes of more than $100,000.
"A Large Black-White Scoring Gap Persists on the SAT" The Journal of Blacks in Higher Education, 2006

The second point made in the above quote is the most important. It means that, though exceptional blacks can make it to the middle and upper middle class, their offspring will tend to sink to lower SES levels, so that, though we will always have a (relatively small) black middle class, blacks who move into the higher SES levels will not be able to establish middle class lineages. The great, and mostly unexamined, hope of the sixties, the establishment of an enduring, hereditary black middle and upper-middle class, can now be seen to be an illusion. See also this:


Posner: "Moreover, because of the bell shape (normal distribution) of IQ across persons, a higher average IQ translates into a much longer upper tail—the part of the distribution that contains the highest IQs."

The shape of the IQ curve is an artefact of the way that IQ test questions are chosen. The choice of a normal distribution is primarily a matter of convenience.

Here is the Godfather of IQ testing on the subject:

Item difficulty [in a mental test] is completely under the test constructor's control....Hence, in constructing a test it is possible, within broad limits, to produce almost any desired form of frequency distribution of the raw scores in a given population. If we have no basis for arguing that the obtained scores have true measurement properties in addition to merely having a rank-order correlation with the latent trait that they measure (and this seems to be typically the case for psychometric test scores) the precise form of the obtained score distribution is essentially arbitrary. The very most that we can say in this case is that (within the limits of measurement error) our test scores have some monotonic relation to whatever the test really "measures." If we could truly measure whatever latent variable, such as g, accounts for the variation in the obtained scores on an absolute scale (i.e., one having a true zero and additivity of scale intervals), the form of its population distribution could turn out to be quite different from that of the test scores we have actually obtained. Certain forms of distribution are simply more useful than others, psychometrically and statistically, and it is this consideration that mainly determines the form of the distribution test constructors decide to adopt.
Jensen "The g Factor," p 101, note 16.


Byron M. Roth: "In my book The Perils of Diversity: Immigration and Human Nature, I cite a study by Erling E Boe and Sujie Shin, "Is the United States Really Losing the International Horse Race in Academic Achievement?” (Phi Delta Kappen, 86,9, May 2005, 688-695, online at: http://www.lowellamrine.com/wbqust/documents/BOE.pdf. Quoting the authors:

"...If these [black and Hispanic students] were to perform at the same level of white students, the U.S. would lead all the other G7 nations (including Japan) in reading and would lead the Western G5 nations in mathematics and science, though it would still trail Japan in these subjects."

Steve Sailer has done an excellent job of analyzing the PISA results, see:

"PISA Scores Show Demography Is Destiny In Education Too—But Washington Doesn’t Want You To Know"

Scroll down to the graph; US performance, combined and broken down by race, is shown by the red lines.

It is inevitable that, as the national proportion of Hispanic students increases, the US average in international tests will decrease. This will lead to more hand-wringing among the elite and for further demands that we spend more money to "fix the schools". The underlying cause will of course never be acknowledged.


EKurtz, Jensen spends the next pages after your quote arguing that general intelligence is indeed normally distributed in a population.


It is very interesting to discover that the white population in the US scored higher than whites in European countries. Has anyone begun a study as to why this is? Perhaps higher IQ people are more willing to take risks, as in immigrating and starting a new life?


JL: "Jensen spends the next pages after your quote arguing that general intelligence is indeed normally distributed in a population."

It seemed to me that Posner was treating the normal distribution of IQ as a *discovery*, which it clearly is not, unlike, say, the normal distribution of height. Jensen's argument that g is Gaussian is not numeric; it depends primarily on the (reasonable) belief that, like height, the genetic determination of IQ involves contributions from multiple independent loci, which is known to give rise to that sort of distribution. But this is an argument from plausibility, not a scientific verification.
As Jensen says
"Most psychometricians implicitly work on the statistically advantageous assumption of normality, and no argument has yet come forth that it is theoretically implausible or adversely affects any practical uses of g-loaded tests. But the question is mainly of scientific interest, and a really satisfactory answer to it cannot come about through improved measurement techniques per se, but will become possible only as part and parcel of a comprehensive theory of the nature of g. "

There are good reasons to believe that the right hand (ie higher) portion of the IQ distribution conforms to the normal model. As Posner put it: "a higher average IQ translates into a much longer upper tail-the part of the distribution that contains the highest IQs". If mental ability (for which IQ is a proxy) is normally distributed, then a population with a higher average IQ will demonstrate greater competency in cognitively difficult areas than one with a lower average - ie we can predict the high IQ performance of a group from its average. This is clearly evident in the different levels of success of, say blacks and Ashkenazi Jews in science and technology. Ashkenazi Jews are major recipients of Nobels in science, whereas blacks are relatively absent from scientific and technical fields, except in the movies.

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Posner peers into the woods and notes "white and Asians" are "already doing fine; for the most part". He could as well peer into the suburbs and find that "blacks" and Hispanics in those areas are doing pretty well too. He could then peer into the areas of substandard funding with worn out schools and aging textbooks and find "whites, blacks" and Hispanics not faring well in both urban and rural areas.

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Well that's right that IQ is understood to reflect both genetic endowment and environmental factors, particularly factors operative very early in a child’s life, including prenatal care, maternal health, the educational level of the parents, family stability, and poverty..


I doubt that we can limit immigration of "unskilled" while living next door to an impoverished nation now wracked by the further corruption from the industry of supply our drug needs.

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American schools, despite Arne Duncan’s claims, are performing well. US-educated Asians scored 541 in contrast with the Japanese, who scored 520. US-educated whites scored 525 in contrast with Germans, who scored 497. US-educated Hispanics scored 466 in contrast with Mexicans, who scored 425. No data was apparently collected in sub-Saharan countries.


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Well Becker points out that despite the imperfections of its educational system, America remains preeminent in innovation. This is important but it appears to be due in part to the nation’s attractiveness to immigrants. Many of our innovators are foreign born; increasingly they are Asian..


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Well good post..Thanks for pointing out the obsession with class size. As if whether one gets to ask one question per day in a 20 student class is really that much different than asking one question per week in a 300 student amphitheate.

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