I promised last time to try to say what is in this book
but my review is getting as long as the book so I will
give only Part I this time and continue next time.
INTRODUCTION
Tests to measure intelligence (called cognitive ability
here) play a central role in this book. Thus, in their
introduction, the authors discuss the history and the
controversies surrounding attempts to measure
intelligence. Modern theory traces its beginnings to
Spearman. Spearman noticed that performances on tests
attempting to measure intelligence were positively
correlated. To explain this, he postulated the existence
of a single variable that he called g which is a persons
general intelligence. It is a quantity like height or
weight that a person has and that varies from person to
person. When you take a test to measure intelligence
your score is a weighted sum ag + bs + e of the
factors g , s, and e with g your general intelligence,
s a measure of your intelligence relating to this
particular test and e a random error. If you take
several different tests, g is common to all of them
and causes the positive correlation. The magnitude
of a tells you how heavily the test is "loaded" with
general intelligence -- the more the better. This
simple model is only consistent with a very special
class of correlation matrices (those with rank 1) and so
had to be generalized to include more than one kind of
g. This led to the development of factor analysis as a
mathematical model for what is going on. It also led to
the development of IQ tests to measure intelligence.
The controversies over the use of IQ began when it
was proposed that they be used to justify sterilization
laws in an attempt to eliminate mental retardation, and
immigration laws to favor the Nordic stock. It
continued when Arthur Jensen suggested that remedial
education programs (begun in the War on Poverty) did not
work because they were aimed at children with relatively
low IQ, largely inherited and therefore difficult to
change. Then followed debates over whether differences
in IQ were due mostly to genetic difference or to
differences in environment culminating in Stephen Jay
Gould's best seller "The Mismeasure of Man". Gould
concluded that "deterministic arguments for ranking
people according to a single scale of intelligence, no
matter how numerically sophisticated, have recorded
little more than social prejudice." While the authors
admit that Gould's ideas still reflect a strong public
sentiment about IQ tests, they feel that it bears very
little relation to the current state of knowledge among
scholars in the field.
Finally, the authors discuss current attempts to
understand intelligence, describing three different
schools.
THE CLASSISTS: intelligence as a structure.
This school continues to extend the work of Spearman
using factor analysis and assuming, as Spearman did,
that some kind of general intelligence is associated
with each individual. Workers in this school continue
to try to understand the physiological basis for the
variables identified by factor analysis and to
improve methods of measuring general intelligence.
THE REVISIONISTS: intelligence as information
processing.
This school tries to figure out what a person is doing
when exercising intelligence, rather than what elements
of intelligence are being put together. A leading
worker in this field, Robert Sternberg writes: "Of
course a tester can always average over multiple scores.
But are such averages revealing, or do they camouflage
more than they reveal? If a person is a wonderful
visualizer but can barely compose a sentence, and
another person can write glowing prose but cannot begin
to visualize the simplest spatial images, what do you
really learn about those two people if they are reported
to have the same IQ?"
THE RADICALS: the theory of multiple intelligences.
This school led by Howard Gardner, rejects the notion of
a general g and argues instead for seven distinct
intelligences: linguistic, musical, logical-
mathematical, spatial, bodily-kinesthetic, and two forms
of "personal" intelligence. Gardner feels that there
is no justification for calling musical ability a
talent and language and logical thinking intelligence.
He would be happy calling them all talents. He claims
that the correlations that lead to the concept of g come
precisely because the tests are limited to questions
that call on these two special aspects of
intellegence.
Herrnstein and Murray consider themselves classists and
state that, despite all the apparent controversies, most
workers in the field of psychometrics would agree with
the following six conclusions that they feel are
consequences of classical theory.
(1) There is such a thing as cognitive ability
on which humans differ.
(2) All standardized tests of academic aptitude
or achievement measure this general factor
to some degree, but IQ tests expressly
designed for that purpose measure it most
accurately.
(3) IQ scores match, to a first degree, whatever
it is that people mean when they use the work
intelligent or smart in ordinary language.
(4) IQ scores are stable, though not perfectly
so, over much of a person's life.
(5) Properly administered IQ tests are not
demonstrably biased against social economic,
ethnic, or racial groups.
(6) Cognitive ability is substantially
heritable, apparently no less than 40
percent and no more than 80 percent.
The authors stress that IQ tests are useful in studying
social phenomena but are "a limited tool for deciding
what to make of any individual."
THE DATA USED IN THIS BOOK
Throughout the book the authors make use of data from
the National Longitudinal Survey of Youth (NLSY) started
in 1979. This was a representative sample of 12,686
persons ages 14 to 21 in 1979. This group has been
interviewed annually and the authors use the data
collected through 1990.
REVIEWER NOTE
While this study was meant to follow labor trends, a
number of other groups used the subjects for their
studies. One of these provided the IQ data necessary
for this book. The army had been using a test called the
Armed Services Vocational Battery (ASVB) since 1950 to
help in the selection of recruits and for special
assignments. It had been suggested that the volunteer
army was selecting a group less well qualified than the
Army obtained by the draft. To check this they decided
to administer the ASVB to the sample chosen for the
NLSY. This study was called the Youth Profile and was
administered by the National Opinion Research Council.
The results showed that the volunteer army was getting a
higher quality army, as measured by these tests, than
the draft, but at the same time found significant
differences between the performance of various ethnic
groups. A study of these differences and a summary of
explanations for them are provided in "The profile of
American youth : demographic influences on ASVAB test
performance" by R. Darrell Bock and Elsie G.J. Moore.
It is interesting to compare their analysis with that of
the authors of this book.
The ASVB has ten subtests which vary from tests you
might find on an IQ vocational test, such as automobile
repair and electronics. The Armed Forces Qualification
Test (AFQT) is made up of the four subtests of the
ASVB: word knowledge, paragraph comprehension,
arithmetic reasoning, mathematical knowledge. The
authors show in an appendix that this test has the
properties of a very good IQ test . In particular, they
found that over 70% of the variance on the AFQT could
be accounted for by a single factor, g, which they
identify with general intelligence.
CHAPTER I. COGNITIVE CLASS AND
EDUCATION 1900-1990
In this part the authors provide a number of graphs that
show there is a cognitive sorting process going on in
education. While many more students are going to
college, a higher and higher proportion of the really
bright students are going to a few select schools. We
see graphs that exhibit the following:
(1) In the twentieth century the prevalence
of college degrees increased rather
continuously from 2% to 33%.
(2) From 1925 to 1950 about the same
percentage (55%) of the top IQ quartile
of the high school graduates went to
college. Starting in 1950, this percentage
increased dramatically from 55% to over
80% in 1980
(3) In 1930 the mean IQ scores for all
those attending college were about .7
standard deviations above the mean and
those attending Ivy League and Seven
Sisters colleges were about 1.3 standard
deviations above the mean. In 1990 the
mean IQ for all attending college had
remained about same a .8 standard deviations,
while the mean IQ for the Ivy League and
Seven sisters mean had increased to 2.7
standard deviations above the mean.
Since these graphs display standardized scores, the
authors spend some time explaining the concepts of mean
and standard deviation in the test and provide a more
complete discussion in an appendix.
The authors express the fear that the clustering of the
high IQ students in a small number of colleges will make
them isolated from and unaware of the real world.
CHAPTER 2. COGNITIVE PORTIONING BY
OCCUPATION
The point of this chapter is that jobs sort people by
cognitive ability in much the same way that colleges do.
A group of twelve professions: accountants, architects,
chemists, college teachers, dentists, engineers,
lawyers, physicians, computer scientists,
mathematicians, natural scientists, social scientists
are considered to be "high-IQ professions". The mean IQ
of people entering these professions is said to be about
120, which is cutoff point for the top decile by IQ.
The authors provide a graph showing that, until 1950,
about 12% of the top IQ decile were in these jobs. Then
the percentage significantly increased, reaching about
38% in 1990. They link this to education with another
graph showing that the proportion of the CEO's with
graduate training remained around 10% until 1950 when
the proportion increased dramatically to about 60% in
1976. Combining these observations the authors
conclude that, at mid-century, the bright people were
scattered throughout the labor force but, as the century
draws to a close, a very high proportion of these people
are concentrated within a few occupations paralleling
the cognitive portioning by education.
CHAPTER 3. THE ECONOMIC PRESSURE TO
PARTITION
This chapter is devoted to showing that IQ is a good
predictor of job performance. It is the first use of
correlation, and an appendix devoted to explaining the
concept of correlation is available for the reader not
familiar with this concept.
The authors discuss a number of studies showing that the
correlation between IQ and job performance is typically
at least .4 and often more. They point out that the
military offers huge data sets for these studies, since
everyone in the military must take the ASVB tests (and
hence also the AFQT IQ test ) and members of the
military attend training schools where they are measured
for "training success" at the end of their schooling,
based on measures that amount to job assessment skills
and knowledge. In these studies, the average correlation
between IQ and job performance is about .6. By looking
at the high correlation between the g factor for the IQ
test and job performance, they conclude that the g
factor is the key to success in these jobs.
Modern studies in the civilian population are typically
done by meta-analysis of small studies leading to
results similar to those found in the military studies.
An exception was in a report of the National Academy of
Sciences "Fairness in Employment Testing", which
reported a correlation of only about .25. The authors
suggest that this is because researchers for this study
did not apply corrections for restricted range which
they feel was appropriate for the purposes of their
study. (Restricted range means that your sample
did not include reasonable numbers from the entire
range of possible scores). When these corrections are
made they say that the correlation would increase to
around .4, consistent with other studies.
The authors also compare various predictors for job
performance and report the results of a study that
showed that the highest correlation between a predictor
and job performance rating was the cognitive test score
(.53) followed by biographical data (.37), reference
checks (.26), education (.22), interview (.14), college
grades (.11) and interest (.10).
The chapter concludes by remarking that the Supreme
Court decision of Griggs v. Duke Co. in 1971, which
severely limited the use of IQ tests for job selection,
is costing the American economy billions of dollars.
REVIEWER NOTE.
The main issues referred to in the Griggs v. Dude
decision is the possibility of so-called "disparate-
impact" lawsuits. These are lawsuits that challenge
employment practices that unintentionally but
disproportionately affect people of a particular race,
color, religion, sex or national origin.
The supreme court has twice changed the ground rules set
up in the Griggs v. Duke decision. The current rules
related to these suits are governed by the Civil Rights
act of 1991. According to this law, if a plaintiff
shows that a specific part of the employment practice
disproportionately affects a particular group, then the
employer must be able to demonstrate that the employment
practice or criterion in question is consistent with a
business necessity (whatever that means).
In order to prove disparate impact using statistical
comparisons, the comparison must be with racial
compositions of the qualified people in the work force,
not the racial composition of the entire work force.
When multiple employment criteria are required and it
can be argued that they cannot be separated, then the
entire employment process may be challenged if it can be
shown to have a disproportionate effect on a particular
group.
For a more detailed discussion of this legislation see
"New Act Clarifies Disparate Impact Law", Casey and
Montgomery, The National Law Journal , March 9, 1992.
CHAPTER 4. STEEPER LADDERS, NARROWER GATES
To illustrate the concept of steeper ladder, narrower
gate we are provided a graph showing that the salary of
Engineers was rather constant from 1930 to 1953, at
about $30,000, and then increased dramatically to about
$70,000 in 1960. During the same period, the salaries
for manufacturing employees showed only a gradual
increase from $10,000 to $20,000.
The authors point out that the labor statistics have
pointed to a mysterious "residual" in trying to account
for the increased spread that occurred in real wages
between 1963 and 1987, even after taking into account
education, experience, and gender. Not surprisingly
they suggest a case for IQ being this residual.
The authors also, in this chapter, deal with the issue
of heritability of IQ. They describe the various kinds
of studies which have been used to study this problem.
They remark that the technical issues in measuring
heritability are too formidable to get into, so they only
explain how heritability is measured in one important
special case, namely in studies of identical twins
reared apart. Here, since the twins have identical
genes and different environments it seems reasonable to
define the heritability to be the correlation between
the twins' IQ scores, which is found to be around .75.
They say that other studies typically provide lower
values for heritability but seldom under .4.