Stephen,
As to Ian Hacking's criticisms of IQ tests, I could even help strengthen
his case by suggesting that another curve is possible. An intelligence test
could possibly be devised that would yield a distribution curve with two
humps.
But Hacking is confusing the arbitrariness of IQ tests (and their
subsequent normalisation) and artificiality. A typical IQ test is a
collection of four or five different types of test and, in the sense that
the results are composited in various ways in order to produce a
symmetrical bell curve, it is an arbitrary collection.
But the result of such a test is still meaningful in the same way, say,
that an Olympic Decathlon event is meaningful even though it is a rather
arbitrary selection of different sorts of physical contests. If I had to
choose a football team or fight a battle I would do well to choose from
among individuals who scored well in decathlon events rather than from
people of average physical abilities. Furthermore, well-designed IQ tests,
like decathlon events, test skills which show high heritability between
parents and children, identical twins, etc. Difficult though intelligence
is to define, it is this heritability factor which can't be explained away.
In fact, purely chronometric tests (reaction times to simple stimuli) are
highly correlated to normal IQ tests.
As to Alexis de Tocqueville's observations of height differentials between
aristocracy and peasantry, yes, there probably would have been hardly any
genetic contribution here. A restricted diet produces smaller mothers who
have small babies, and so on (for ever, while the diet stays the same).
When the diet improves, however, peasant mothers can grow a little larger
and can carry slightly larger babies. This sort of recovery takes anything
up to six or more generations. (For example, European man took about 200
years to finally arrive, by about 1960, at the normal height and weight of
neolithic man. Many modern Japanese, Koreans and Chinese have not yet fully
recovered their true genetic height.)
As to social division, well I suppose we'd both agree that there's a
well-documented difference in height, weight, appearance and ability
between, say, Oxbridge undergraduates and others of the same age -- or
between middle-class and working-class children . A hundred years ago, most
of this divide could be attributable to social/nutritional effects. Today,
I'd suggest that there's an IQ component also. And the more egalitarian,
uniform and selective the educational experience becomes then the greater
will be the genetic component.
It's easy to see the divide (at least it is in England -- simply by knowing
what national newspapers they buy) though it's far less easy to determine
the components of IQ and social factors at the margins. There'll be pseudo
intellectuals in the quality newspaper readership and, in the "lower"
group, genuinely brilliant individuals who somehow don't realise that
they're far brighter than they imagine -- at least until they reach their
30s and 40s. (I used to know a lot of these sorts in factory life 35 years
ago, but they're less likely today.)
Keith Hudson
At 06:06 03/11/02 -0800, you wrote:
>Mike H:
>>> There are reasons why the bell curve is used in intelligence testing -
>>> population intelligence fits it.
>
>Keith H:
>> The Bell curve isn't 'used' in intelligence testing -- it's a consequence
>> of it.
>
>Stephen S:
>
>No, it is a consequence of test design. It is **assumed**
>that this thing ("IQ" or "g") occurs in a population
>according to a Guassian distribution (which is *to assume*
>that it has the same distribution as many biological traits
>and thus is demonstrably just as real and a proper object of
>measurement). This is the *rhetorical* force of IQ fitting a
>bell curve. But this fit is not a fact; it's an artifact. An
>IQ test that does NOT give a bell curve IS A FAULTY TEST and
>must be REVISED. It has to be "normalized".
>
>There are THREE kinds of Bell Curves according to Ian
>Hacking (and it seems to me he's quite right).
>
>Here is an excerpt from Hacking's review of Herrnstein &
>Murray's _The Bell Curve_ (_London Review of Books_, 26 Jan.
>1995, p. 5). Hacking offers the following "pedantic remarks"
>to clarify H&M's assertion that "It makes sense that most
>things will be arranged in bell-shaped curves. Extremes
>tend to be rarer than the average."
>
>"[The authors] do not note that there are three distinct
>kinds of bell.
>
>"1. THE CURVE OF ERRORS. Around 1800, some of the greatest
>mathematicians of the day, such as Gauss and Laplace,
>proposed a highly plausible mathematical model of the
>distribution of errors made by an observer using an
>instrument to determine the position of an object such as a
>heavenly body. There was a real, true unknown value. If the
>measurements were unbiased, their average, or mean, would be
>that value, and the curve of error modelled the deviation
>around that real true value.
>
>"2. BIOMETRIC DISTRIBUTIONS. About fifty years later a
>Belgian astronomer, Quetelet, noted that measurements of
>many biological variables are distributed like the curve of
>errors. His first example was the chest circumference of
>soldiers in Highland regiments; Murray and Herrnstein use
>the heights of boys in your high-school gym class... Notice
>that the mean is no longer aiming at a measure of a real
>quantity existing in nature, but is just an average, and
>that the deviation around the mean is *not* produced by
>physical or geometrical symmetries in the measuring device
>plus observer. Karl Pearson, often called the founder of
>biometrics, was so convinced that these distributions were
>widespread that he called them *normal*. In most other
>languages they are still called "Gaussian". Pearson's mentor
>and patron, Francis Galton, inventor of regression and
>correlation, long warned against trying to fit all
>biometrical distributions into the 'Procrustean Bed' of the
>error curve.
>
>"3. NORMALISED TEST RESULTS. Because many real biometric
>variables such as height are distributed like the curve of
>errors, it was supposed that postulated quantities should
>follow the same curve. IQ is the classic example.
>Questions were chosen so that (in the simplest case) half
>the population being tested would answer correctly, giving a
>mean score of 100. The skill of designing a test was, in
>part, to choose questions so that the results in the
>population formed, roughly, a Gaussian curve. If they did
>not, change the questions. The greatest designer of tests
>was Lewis Terman, who invented the name IQ, and who did the
>first massive testing, of US Army recruits in 1917. When
>attention was turned to women, it emerged that female scores
>were higher than male ones. Solution: find the questions
>that women answer better than men and replace them.
>
>Thus it is a fact of biometrics that males of the same
>population are on average taller than females. But it was
>*not* an empirically discovered fact of nature, revealed by
>Terman's final tests, that females have the same average IQ
>as men. It was a fact of test design. I do not mean this
>observation to impugn the testing industry. I am saying only
>that the bell curve of IQ is a logically different species
>of beast from the bell curve of biometrics, in turn
>logically different from the original bell curve of error. A
>technicality? No, because *one ought to conceptualise
>causality very differently in the three cases*..." [my
>emphases -- SS]
>
>-- END OF HACKING --
>
>
>It seems clear to me that there are myriad difficulties
>around the whole business of IQ (or "g") and especially the
>question of its heritability.
>
>An emerging "IQ divide" may be (or become) a social FACT.
>But if it is (or does) it will still be very hard to know
>the degree to which it is the result of biological
>reproduction rather than social reproduction and it may well
>be technically (if not conceptually) impossible to
>distinguish between the two.
>
>Alexis de Tocqueville observed that the "orders" in *ancien
>regime* France (aristocrats, peasants) have the appearance
>of different "races of men" because their ways of life are
>so different. (On the basis of nutrition alone the peasant
>will be noticeably shorter than the race of his superiors.)
>In the early 19th Century, then, Tocqueville can *observe*
>different races of Frenchmen. Doubtless, many of these
>"racial" traits were highly heritable. But we would surely
>ascribe all or the greatest part of that heritability to
>*social* reproduction, would we not?
>
>(I need to think more about what Keith has been saying about
>the "IQ divide". My hunch is that any such divide can be
>understood and explained in terms of social reproduction
>alone. But I've not got the argument put together. This is
>for another post, another time.)
>
>best wishes,
>
>Stephen Straker
>
><[EMAIL PROTECTED]>
>Vancouver, B.C.
>[Outgoing mail scanned by Norton AntiVirus]
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Keith Hudson,6 Upper Camden Place, Bath BA1 5HX, England
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