yet more Jensen

From: Mike Cole (mcole@weber.ucsd.edu)
Date: Tue Dec 21 1999 - 17:08:06 PST


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Subject: psyc.99.10.072.intelligence-g-factor.14.hunt (478 lines)
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psycoloquy.99.10.072.intelligence-g-factor.14.hunt Tue Dec 21 1999
ISSN 1055-0143 (34 paragraphs,15 references, 472 lines)
PSYCOLOQUY is sponsored by the American Psychological Association (APA)
                Copyright 1999 Earl Hunt

                The Modifiability of Intelligence
                Commentary on Jensen on intelligence-g-factor

                Earl Hunt
                Department of Psychology
                Box 251525
                The University of Washington
                Seattle, WA 98195-1525; USA
                ehunt@u.washington.edu

    ABSTRACT: Jensen asserts that general intelligence (g) exists; that
    it is largely biological and immutable; that racial differences in
    intelligence test scores reflect differences in underlying
    cognitive ability, are genetic in origin, and are probably
    immutable. I argue that one must distinguish between factors
    underlying g. A substantial part of the variation in intelligence
    is biological, but modifiable. Racial differences in cognitive
    skills do exist but they can be modified to some extent by social
    means. The extent to which racial differences are biological is
    unknown at present, and speculation without evidence is unwise.

1. Individual differences in mental competence, 'intelligence' for
short, have been a contentious topic in Psychology for over one hundred
years. The possibility that there may be genetic components to mental
competence is unnerving to people who are strongly committed to a
social egalitarian view of how the world ought to be. This is
particularly a problem for those social egalitarians who, with reason,
are concerned that unfettered development of an individual's wealth and
power may not be all that good for the society as a whole. For that
reason the social egalitarian may want some sort of forced intervention
to rise the less fortunately endowed up to their full potential. This
is a laudable goal, but it implies that the egalitarian knows what the
intervention should be. Add to this the possibility that there are
genetically determined differences in mental competence between races
and ethnic groups, and the possibility that there is not much we can do
about it. The social egalitarian now faces a mortal threat.

2. In 1969 Arthur Jensen published an article in the Harvard
Educational Review (Jensen, 1969) that reviewed the then-existing
evidence indicating that all of these bad things (at least from the
social egalitarian's viewpoint) are true. Jensen's (1998) current book
summarises thirty more years of research, which he concludes
establishes scientific evidence for the existence and importance of
general intelligence, its biological and largely genetic origin, and
the putative genetic origins of differences in cognitive competence
between racial groups. There are no surprises here for anyone who has
followed Jensen's work. Therefore a review of the book provides a
chance to comment on the ideas that Jensen and his not-inconsiderable
group of followers have espoused.

3. Reactions to Jensen's ideas have, predictably, fallen into two
classes. He has been vilified and threatened. 'Jensenism' has, to
some, become a modern term almost on a par with Nazism. Jensen himself,
and a not-inconsequential group of psychometricians, psychologists, and
sociologists, see some of the criticism as attacks on a reputable
scientist whose research has turned up some unpleasant truths. In 1988,
a full issue of the journal Intelligence was devoted to comments on his
work. There he was referred to as a 'King among men' for his unswerving
pursuit of the truth. Now, in The g factor, Jensen makes his own case.
In evaluating it I shall take a middle ground. (There are times when I
feel very lonely doing this.)

4. Jensen's treatise is not a book on Intelligence. It is a book
presenting Jensen's view of intelligence. If you want a text with a
balanced view, use Mackintosh's (1998) even-handed presentation.
However, I do not think that Jensen intended to write a textbook; he
wanted to present a case. His case is built around three themes, and
several subthemes.

5. Jensen's first theme is that there is a general factor in
intelligence. He is undoubtedly correct. Virtually all aspects of
cognitive performance are positively correlated, especially in the
"lower half" of ability. Truly high performance tends to be more
specialised, a point that will be important later. However there can be
no doubt about the statistical finding.

6. Jensen explains the statistical finding by assuming that it reflects
the influence of a pervasive general intelligence, the g factor. It is
not clear that this is the case. After a massive review of the
psychometric literature, Carroll (1993) concluded that intellectual
performance is best characterised by a three-tier theory. At the bottom
are narrowly defined abilities (e.g., speed of word retrieval). Above
that there are broad general factors, most prominently fluid and
crystallised intelligence, and visual-spatial reasoning. For those not
familiar with the terminology, fluid intelligence is, loosely, the
ability to deal with new and unfamiliar problems and crystallised
intelligence is the ability to bring previously acquired problem
solving techniques to bear on the present problem. Because the broad
general factors are statistically associated, you can place a single
factor at the top. A similar argument was made by R. B. Cattell (1971)
and by John Horn (1985; Horn & Noll 1994).

7. The question is whether the correlation between the broad general
factors is causal, because of an underlying general intelligence
factor, or whether it is a statistical artifact, because the second
order factors depend (to different degrees) upon the same underlying
factors, such as pattern recognition, working memory, and the control
of attention. Jensen favours the causal explanation. Others (notably
Horn) do not. I side with Horn, and here is why.

8. In experimental psychology one of the ways of showing that two
behaviours are reflections of different causal mechanisms is to show
that there are independent variables that affect the two behaviours in
different ways. The same logic is used in neuropsychology, where the
independent variable is brain damage and the phenomenon is called
double dissociation. There are two areas in which interactions between
types of intelligence tests and other variables have been well
established. The first is ageing. It is well known that over the adult
years scores on fluid intelligence tests drop. On the other hand,
scores on verbal comprehension and general knowledge tests increase or
stay constant until old age. Next, suppose we look at the cohort
effect, the fact that, with age held constant, test scores have been
rising in the industrial nations over the past fifty years (Flynn,
1987; Hertzog, 1994). Scores on tests that measure fluid intelligence
have risen substantially. Scores that emphasise crystallised
intelligence, and scores on acquired problem solving skills, such as
text comprehension, have shown little if any rise.

9. If a neuropsychologist were to observe these patterns in patients
characterised by different types of brain damage, the neuropsychologist
would conclude that the behaviours were subsumed by different brain
systems. I suggest that these interactions, observed on a societal
rather than an individual basis, constitute substantial evidence for
distinct second order cognitive talents that are statistically but not
causally linked.

10. Another of Jensen's arguments for the causal nature of general
intelligence is that intelligence test scores are correlated with a
variety of elementary cognitive tasks, most notably reaction time and
inspection time tasks. This is consistent with Carroll's conclusions
regarding three levels of cognitive abilities. The facts are clear.
Jensen goes beyond the facts to conclude that these correlations
reflect basic physiological processes associated with neural
efficiency. This conclusion bothers me, because there are two major
holes in the evidence.

11. First, the elementary cognitive tasks do not seem to be closely
correlated with each other. If Jensen's argument is correct they
should be. (However I think we need much more evidence before a
definitive statement can be made.) Second, much of the evidence for
reaction time correlations rests on studies by Jensen and his
colleagues using a particular procedure, which he describes in detail.
The important thing about this procedure is that Jensen provides many
fewer practice trials than is customary in reaction time research.
(You have to go back to the original literature to see this, and of
course the exact statement varies with the study in question. However,
strong practice effects have been observed using Jensen's procedures
and apparatus (Widaman and Carlson, 1989). What Jensen's procedure may
be picking up is a bit of fluid intelligence as the participant tries
to figure out how to work the gadget the psychologist designed. Also,
suppose that we accept Jensen's argument that elementary cognitive
tasks correlate with intelligence tests because both depend on neural
efficiency. If this were true, then the correlations between
intelligence test scores and reaction time tasks should go up over
practice, for as the participant figures out how to work the apparatus
his or her performance should depend more and more on neural efficiency
limits rather than strategy choices. But the opposite occurs, over
extended practice the correlations between intelligence test scores and
elementary task performance go down (Ackerman, 1989). This is a serious
embarrassment for Jensen's approach.

12. Having said this, are the different varieties of intelligence
important? You bet they are. Psychometric tests of cognitive ability
are generally the best predictors that we have of both academic and
workplace performance. They far outperform personality tests, and are
only equalled by carefully structured interviews or by work samples.
Jensen is quite correct in emphasising the importance of whatever is
evaluated by the tests.

13. Jensen's second theme, genetics as a cause of intelligence, is his
second most contentious point. Massive studies have shown that genetics
accounts for about half of the variance in test performance. The
effects seem to be highest in childhood and then again in great age.
Jensen often refers to 'adults.' This is a bit misleading. The evidence
for the post-sixty generations is strong. The data for individuals in
their working years (25-60) are sparse, for the simple reason that it
is very hard to get a representative sample of working adults. They are
too busy to sit down for psychological testing.

14. No environmental variable has ever been found that begins to
account for as much variance in test performance as genetic variables.
Now one can always explain this away by reference to unmeasured
variables, but this really will not do. In my own opinion environmental
hypotheses are not going to have much influence until we develop a
theory of the environment that approaches the sophistication of our
theories of genetics. Put another way, I know what percent of my genes
I share with my brother and my cousins. I do not know how to measure
the similarity between their social-intellectual environment and my
own.

15. As is well known, the expression of genetic traits can be altered
by environmental factors. Therefore showing that intelligence is
partly genetically determined does not mean that it cannot be changed.
But how? Jensen claims, with good evidence, that none of our programmes
intended (partially) to alter cognitive skills have had many long term
effects. That is, we do not know how to create an
infant-pre-school-school- work environment that will increase
intelligence.

16. But we do know that some aspects of intelligence can be changed.
First, the existence of the cohort effect shows that intelligence can
be altered, for some changes in our society are altering it. In this
respect, I note, along with Teasdale and Owen (1989) that the primary
cohort gains are at the bottom. That is, we do not have as many low
scorers as we used to. (Gains have been shown at the top, but they are
much smaller.) Also, it is quite clear that schooling affects some of
the test scores that Jensen is willing to accept as appropriate tests
of intelligence. The case has been best made for the data from the
National Longitudinal Study of Youth (NLSY), where it has been shown
that an extra year of schooling does influence scores on the Armed
Forces Vocational Aptitude Battery (ASVAB) (Cawley et al., 1997). This
is hardly surprising to anyone who knows what is on the ASVAB, a lot of
its content is related to school subjects. Because Jensen is willing to
commit himself to the ASVAB, and to the NLSY data set, when it suits
his purposes, he must deal with the schooling effects demonstrated for
this test and data set.

17. Parenthetically, I believe that the schooling effects and the
cohort effect may be related. Since World War II every industrialised
nation has increased its requirements for mandatory education and has
gone to great lengths to reduce drop-outs and to offer 'second chance'
schooling for adults who do drop out. Given the amount of money spent,
one hopes that there would be an effect on people in the lower range of
test scores. Apparently such an effect exists.

18. To sum up this part of the argument, Jensen is right in stating
that intelligence has a strong genetic component. He is probably wrong
in saying that intelligence cannot be altered, but right in saying that
we do not know how to alter it. Certainly the present evidence suggests
that massive early childhood intervention may have only a transitory
effect on cognitive skills. But may I point out that providing every
child with a safe, healthy, supportive environment is a good thing to
do, regardless of whether or not it affects their IQ test score ten
years later?

19. The third theme is race. Jensen's position on racial differences in
intelligence is by far the most contentious issue in this book and in
his career. While it is hard to separate the scientific, political, and
social issues I shall try.

20. Jensen's argument has changed very little since his famous (or
infamous, depending on your view) Harvard Educational Review article
thirty years ago. He asserts that there is an I.Q. score gap of
slightly over one standard deviation unit between White and African-
Americans, that the gap is constant, that it reflects real differences
in cognitive skills and, in this book, that the gap is largely
genetic. He admits that solid proof for the last statement is lacking,
but he claims that genetic causation should be the 'default hypothesis'
until it is disproved.

21. If you combine Jensen's beliefs about racial differences with his
belief about the immutability of intelligence, you are forced to the
conclusion that some racial groups are unchangeably more cognitively
competent than others. Does Jensen accurately present the data, and is
the default hypothesis a useful summary of our scientific
understanding?

22. The test score gap between Whites and African-Americans is real.
Furthermore, it almost certainly reflects a cognitive-skills gap. The
gap appears on tests that are intentionally designed to measure
cognitive skills related to the workplace, such as the National
Assessment of Educational Progress (NAEP). The gap is important, for
validity studies indicate that the tests predict academic and workplace
performance of minorities about as well as they predict the performance
of Whites.

23. On the other hand, and in contradiction to Jensen's statements, the
gap is clearly decreasing. While the gap varies from test to test, I
think that the fairest summary of the current situation is that the gap
was as much as 1.25 standard deviation units fifty years ago, and is
about .8 units today. Therefore the one standard deviation unit
statement is a good summary of the overall data, but it does ignore a
trend. Also, Jensen cites studies in South Africa, during the apartheid
era, showing a gap of more than two standard deviation units between
White and Black South Africans. He emphasises the size, I would
emphasise the difference between the gap in South Africa in those days
and in the United States today.

24. The fact that the gap is decreasing is in agreement with the cohort
effect. If the main effect of cohort changes has been to increase the
score of the bottom groups, and if African Americans were concentrated
toward the bottom of the distribution fifty years ago, then the
White-African American gap is going to decrease. Since the decrease is
taking place over only a few generations, it is hard to account for the
all of the gap on a genetic basis. Some of it might be genetic, but we
do not know how much.

25. Jensen rests his case for the genetic hypothesis on three facts
about White vs. African American scores, and an inference from a fourth
fact. Test items and tests that have the lowest apparent cultural
loadings (e.g., the Raven Matrix tests) show the greatest disparity
between racial groups. This rules out the hypothesis that the test gap
is due to the test's content differentially favouring the white over
the African-American culture. Test items and tests that show the
highest g loadings also show the greatest disparity between groups.
This suggests to Jensen that the gap is due to racial differences in
general intelligence. And recall that Jensen sees general intelligence
as being largely genetically determined. Finally, the factor structures
obtained from testing in the African American population are
essentially the same as those obtained in the White population. Jensen
combines these observations with the evidence for a genetic basis for
intelligence, largely gathered in the White population, to conclude
that the White-African American gap is also of genetic origin.

26. One can evaluate the evidence in a slightly different way. To me it
appears that the biggest gap is on tests that evaluate fluid
intelligence. This is not a play on words. It may be that we can obtain
some leverage on the general skills gap by finding ways to inculcate
higher degrees of crystallised intelligence, i.e., by better
education. If fluid intelligence is low, a teacher who wishes to raise
students' crystallised intelligence faces a formidable challenge.
Formidable challenges are just that, difficult but not impossible.
Whether or not society wishes to expend the resources to overcome this
challenge is a social, not a scientific, question.

27. The third fact, about the identity of factor structures, seems to
me to be incongruous. Studies completed in both Europe and the U.S. in
the past ten years have shown that the general intelligence factor is
more pervasive at the low end of the distribution than it is at the
high end. Therefore, if the African-American population falls below the
White population intelligence tests should be more saturated with
general intelligence in the African-American than White populations.
However Jensen (pg.374 ff. claims, correctly I believe, that the factor
structures are essentially the same. This is consistent with the
argument that different underlying causes are responsible for
inter-group mean differences and intra-group individual variation.

28. Finally, there is the exclusionary evidence. At present, no one has
produced evidence for a specific environmental or social cause that
could explain racial disparities in intelligence. This is partly
because genetic and social variables are confounded. Should Mother's
Education be used as a surrogate for mother's level of acquired
cognitive status or mother's genetic makeup? It depends on your point
of view. The other part of the difficulty has to do with the
theoretical and practical constraints on the studies. We do not have
good theories of the relation between social psychology and individual
differences; the experimental studies strike me more as investigation
of (sometimes insightful) hunches than careful analyses of theoretical
implications. It is fairly easy to carry out attitudinal studies in
college sophomores, it is much harder to carry out those same studies
with adults, in the workplace, where the problem is.

29. In order to carry out a direct test of Jensen's hypothesis we would
have to know what genes are related to intelligence test scores, and
then determine whether the allele frequencies for those genes differed
in different racial groups. There are excellent reasons for locating
genes related to test scores and, indeed, some such studies have been
carried out. They indicate (no surprise) that there is no one gene for
intelligence, but that there may be hundreds, each of which makes a
small contribution. I am sure there will be steady, but possibly slow,
progress.

30. So, it may be that sometime between 25 and 50 years from now we
will be able to compare allele distributions in different racial
groups. Jensen says that as a default we should assume that there will
be differences. I fail to see any compelling reason for having a
default hypothesis at all. And while I would (and do) support the
studies to identify the relevant genes, I would not put very much money
into the studies to identify different distributions across racial
groups. I do not see what the purpose would be.

31. Suppose that we knew all the allele-intelligence associations, and
suppose further that we could establish an individual's genotype as
easily as we can take fingerprints. Scientifically, any interest will
be in the allele associations and the mechanisms by which the genes
exert their actions, not on the individual's membership in a particular
social group. In terms of social action (including education), any
intervention to deal with that individual would again depend upon his
or her phenotype, not the statistics on genotypes in populations that
the individual might belong to. So why do we need to evaluate, or even
need, Jensen's default hypothesis?

32. Only one reason comes to mind. While Jensen is silent on this
point, others have used his point of view to attack a variety of
affirmative action programs. The attack is based on the argument that
the affirmative action programs are only justified if we believe that
cognitive skills in various groups are really equal, so that social
intervention can realise an unrealised potential. Jensen's point of
view is that the potential is largely not there in affected minority
groups. If you accept this argument, and you believe that the
affirmative action programs are based on an assumption of equality,
then expenditures for these programs are not justified.

33. As I have indicated above, I have reservations about the strong
statement that group differences in cognitive ability are immutable. On
the other hand, there is no compelling reason to believe that no
differences exist; and we simply do not know how much effort it would
take to give everyone, everywhere, an equal opportunity to realise his
or her potential.

34. It follows that we have to make judgement calls about how many
resources to develop in programmes that might work. (A programme that
does not work is simply a pork barrel project.) These judgement calls
occur in the political realm, not the scientific realm. As of the end
of the 20th century American and European societies have a few
'affirmative action' programmes for farmers, and offer tax breaks to
retailers and shoppers on the Internet. The USA supports a special
National Science Foundation programme for women in science and
engineering, and provides taxpayer-financed incentives to the owners of
professional football and baseball teams. It also provides funding to
allow university professors to explore the Antarctic, offers school
lunch programmes to poorer children, and does many other things that
provide advantages for some citizens at the expense of others. In
theory, at least, these programmes are justified on the grounds that
they add to the overall social good. That is the criterion an
affirmative action programme has to meet; will it add to the overall
social good? Jensen's default hypothesis is irrelevant on social as
well as scientific grounds.

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Ability" PSYCOLOQUY 10(23).
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