From: J. R. Molloy (jr@shasta.com)
Date: Tue Sep 04 2001 - 08:00:30 MDT
From: "Chen Yixiong, Eric" <cyixiong@yahoo.com>
> http://www.sciam.com/specialissues/1198intelligence/1198gottfred.html
Good article. Thanks for posting the link.
Here's the text for those without web access.
The General Intelligence Factor
Despite some popular assertions, a single factor for intelligence, called g,
can be measured with IQ tests and does predict success in life
by Linda S. Gottfredson
What Is versus What Could Be
No subject in psychology has provoked more intense public controversy than
the study of human intelligence. From its beginning, research on how and why
people differ in overall mental ability has fallen prey to political and
social agendas that obscure or distort even the most well-established
scientific findings. Journalists, too, often present a view of intelligence
research that is exactly the opposite of what most intelligence experts
believe. For these and other reasons, public understanding of intelligence
falls far short of public concern about it. The IQ experts discussing their
work in the public arena can feel as though they have fallen down the rabbit
hole into Alice's Wonderland.
The debate over intelligence and intelligence testing focuses on the question
of whether it is useful or meaningful to evaluate people according to a single
major dimension of cognitive competence. Is there indeed a general mental
ability we commonly call "intelligence," and is it important in the practical
affairs of life? The answer, based on decades of intelligence research, is an
unequivocal yes. No matter their form or content, tests of mental skills
invariably point to the existence of a global factor that permeates all
aspects of cognition. And this factor seems to have considerable influence on
a person's practical quality of life. Intelligence as measured by IQ tests is
the single most effective predictor known of individual performance at school
and on the job. It also predicts many other aspects of well-being, including a
person's chances of divorcing, dropping out of high school, being unemployed
or having illegitimate children [see illustration].
By now the vast majority of intelligence researchers take these findings for
granted. Yet in the press and in public debate, the facts are typically
dismissed, downplayed or ignored. This misrepresentation reflects a clash
between a deeply felt ideal and a stubborn reality. The ideal, implicit in
many popular critiques of intelligence research, is that all people are born
equally able and that social inequality results only from the exercise of
unjust privilege. The reality is that Mother Nature is no egalitarian. People
are in fact unequal in intellectual potential--and they are born that way,
just as they are born with different potentials for height, physical
attractiveness, artistic flair, athletic prowess and other traits. Although
subsequent experience shapes this potential, no amount of social engineering
can make individuals with widely divergent mental aptitudes into intellectual
equals.
Of course, there are many kinds of talent, many kinds of mental ability and
many other aspects of personality and character that influence a person's
chances of happiness and success. The functional importance of general mental
ability in everyday life, however, means that without onerous restrictions on
individual liberty, differences in mental competence are likely to result in
social inequality. This gulf between equal opportunity and equal outcomes is
perhaps what pains Americans most about the subject of intelligence. The
public intuitively knows what is at stake: when asked to rank personal
qualities in order of desirability, people put intelligence second only to
good health. But with a more realistic approach to the intellectual
differences between people, society could better accommodate these differences
and minimize the inequalities they create.
Extracting g
Early in the century-old study of intelligence, researchers discovered that
all tests of mental ability ranked individuals in about the same way. Although
mental tests are often designed to measure specific domains of
cognition--verbal fluency, say, or mathematical skill, spatial visualization
or memory--people who do well on one kind of test tend to do well on the
others, and people who do poorly generally do so across the board. This
overlap, or intercorrelation, suggests that all such tests measure some global
element of intellectual ability as well as specific cognitive skills. In
recent decades, psychologists have devoted much effort to isolating that
general factor, which is abbreviated g, from the other aspects of cognitive
ability gauged in mental tests.
The statistical extraction of g is performed by a technique called factor
analysis. Introduced at the turn of the century by British psychologist
Charles Spearman, factor analysis determines the minimum number of underlying
dimensions necessary to explain a pattern of correlations among measurements.
A general factor suffusing all tests is not, as is sometimes argued, a
necessary outcome of factor analysis. No general factor has been found in the
analysis of personality tests, for example; instead the method usually yields
at least five dimensions (neuroticism, extraversion, conscientiousness,
agreeableness and openness to ideas), each relating to different subsets of
tests. But, as Spearman observed, a general factor does emerge from analysis
of mental ability tests, and leading psychologists, such as Arthur R. Jensen
of the University of California at Berkeley and John B. Carroll of the
University of North Carolina at Chapel Hill, have confirmed his findings in
the decades since. Partly because of this research, most intelligence experts
now use g as the working definition of intelligence.
The general factor explains most differences among individuals in performance
on diverse mental tests. This is true regardless of what specific ability a
test is meant to assess, regardless of the test's manifest content (whether
words, numbers or figures) and regardless of the way the test is administered
(in written or oral form, to an individual or to a group). Tests of specific
mental abilities do measure those abilities, but they all reflect g to varying
degrees as well. Hence, the g factor can be extracted from scores on any
diverse battery of tests.
Conversely, because every mental test is "contaminated" by the effects of
specific mental skills, no single test measures only g. Even the scores from
IQ tests--which usually combine about a dozen subtests of specific cognitive
skills--contain some "impurities" that reflect those narrower skills. For most
purposes, these impurities make no practical difference, and g and IQ can be
used interchangeably. But if they need to, intelligence researchers can
statistically separate the g component of IQ. The ability to isolate g has
revolutionized research on general intelligence, because it has allowed
investigators to show that the predictive value of mental tests derives almost
entirely from this global factor rather than from the more specific aptitudes
measured by intelligence tests.
In addition to quantifying individual differences, tests of mental abilities
have also offered insight into the meaning of intelligence in everyday life.
Some tests and test items are known to correlate better with g than others do.
In these items the "active ingredient" that demands the exercise of g seems to
be complexity. More complex tasks require more mental manipulation, and this
manipulation of information--discerning similarities and inconsistencies,
drawing inferences, grasping new concepts and so on--constitutes intelligence
in action. Indeed, intelligence can best be described as the ability to deal
with cognitive complexity.
This description coincides well with lay perceptions of intelligence. The g
factor is especially important in just the kind of behaviors that people
usually associate with "smarts": reasoning, problem solving, abstract
thinking, quick learning. And whereas g itself describes mental aptitude
rather than accumulated knowledge, a person's store of knowledge tends to
correspond with his or her g level, probably because that accumulation
represents a previous adeptness in learning and in understanding new
information. The g factor is also the one attribute that best distinguishes
among persons considered gifted, average or retarded.
Several decades of factor-analytic research on mental tests have confirmed a
hierarchical model of mental abilities. The evidence, summarized most
effectively in Carroll's 1993 book, Human Cognitive Abilities, puts g at the
apex in this model, with more specific aptitudes arrayed at successively lower
levels: the so-called group factors, such as verbal ability, mathematical
reasoning, spatial visualization and memory, are just below g, and below these
are skills that are more dependent on knowledge or experience, such as the
principles and practices of a particular job or profession.
Some researchers use the term "multiple intelligences" to label these sets of
narrow capabilities and achievements. Psychologist Howard Gardner of Harvard
University, for example, has postulated that eight relatively autonomous
"intelligences" are exhibited in different domains of achievement. He does not
dispute the existence of g but treats it as a specific factor relevant chiefly
to academic achievement and to situations that resemble those of school.
Gardner does not believe that tests can fruitfully measure his proposed
intelligences; without tests, no one can at present determine whether the
intelligences are indeed independent of g (or each other). Furthermore, it is
not clear to what extent Gardner's intelligences tap personality traits or
motor skills rather than mental aptitudes.
Other forms of intelligence have been proposed; among them, emotional
intelligence and practical intelligence are perhaps the best known. They are
probably amalgams either of intellect and personality or of intellect and
informal experience in specific job or life settings, respectively. Practical
intelligence like "street smarts," for example, seems to consist of the
localized knowledge and know-how developed with untutored experience in
particular everyday settings and activities--the so-called school of hard
knocks. In contrast, general intelligence is not a form of achievement,
whether local or renowned. Instead the g factor regulates the rate of
learning: it greatly affects the rate of return in knowledge to instruction
and experience but cannot substitute for either.
The Biology of g
Some critics of intelligence research maintain that the notion of general
intelligence is illusory: that no such global mental capacity exists and that
apparent "intelligence" is really just a by-product of one's opportunities to
learn skills and information valued in a particular cultural context. True,
the concept of intelligence and the way in which individuals are ranked
according to this criterion could be social artifacts. But the fact that g is
not specific to any particular domain of knowledge or mental skill suggests
that g is independent of cultural content, including beliefs about what
intelligence is. And tests of different social groups reveal the same
continuum of general intelligence. This observation suggests either that
cultures do not construct g or that they construct the same g. Both
conclusions undercut the social artifact theory of intelligence.
Moreover, research on the physiology and genetics of g has uncovered
biological correlates of this psychological phenomenon. In the past decade,
studies by teams of researchers in North America and Europe have linked
several attributes of the brain to general intelligence. After taking into
account gender and physical stature, brain size as determined by magnetic
resonance imaging is moderately correlated with IQ (about 0.4 on a scale of 0
to 1). So is the speed of nerve conduction. The brains of bright people also
use less energy during problem solving than do those of their less able peers.
And various qualities of brain waves correlate strongly (about 0.5 to 0.7)
with IQ: the brain waves of individuals with higher IQs, for example, respond
more promptly and consistently to simple sensory stimuli such as audible
clicks. These observations have led some investigators to posit that
differences in g result from differences in the speed and efficiency of neural
processing. If this theory is true, environmental conditions could influence g
by modifying brain physiology in some manner.
Studies of so-called elementary cognitive tasks (ECTs), conducted by Jensen
and others, are bridging the gap between the psychological and the
physiological aspects of g. These mental tasks have no obvious intellectual
content and are so simple that adults and most children can do them accurately
in less than a second. In the most basic reaction-time tests, for example, the
subject must react when a light goes on by lifting her index finger off a home
button and immediately depressing a response button. Two measurements are
taken: the number of milliseconds between the illumination of the light and
the subject's release of the home button, which is called decision time, and
the number of milliseconds between the subject's release of the home button
and pressing of the response button, which is called movement time.
In this task, movement time seems independent of intelligence, but the
decision times of higher-IQ subjects are slightly faster than those of people
with lower IQs. As the tasks are made more complex, correlations between
average decision times and IQ increase. These results further support the
notion that intelligence equips individuals to deal with complexity and that
its influence is greater in complex tasks than in simple ones.
The ECT-IQ correlations are comparable for all IQ levels, ages, genders and
racial-ethnic groups tested. Moreover, studies by Philip A. Vernon of the
University of Western Ontario and others have shown that the ECT-IQ overlap
results almost entirely from the common g factor in both measures. Reaction
times do not reflect differences in motivation or strategy or the tendency of
some individuals to rush through tests and daily tasks--that penchant is a
personality trait. They actually seem to measure the speed with which the
brain apprehends, integrates and evaluates information. Research on ECTs and
brain physiology has not yet identified the biological determinants of this
processing speed. These studies do suggest, however, that g is as reliable and
global a phenomenon at the neural level as it is at the level of the complex
information processing required by IQ tests and everyday life.
The existence of biological correlates of intelligence does not necessarily
mean that intelligence is dictated by genes. Decades of genetics research have
shown, however, that people are born with different hereditary potentials for
intelligence and that these genetic endowments are responsible for much of the
variation in mental ability among individuals. Last spring an international
team of scientists headed by Robert Plomin of the Institute of Psychiatry in
London announced the discovery of the first gene linked to intelligence. Of
course, genes have their effects only in interaction with environments, partly
by enhancing an individual's exposure or sensitivity to formative experiences.
Differences in general intelligence, whether measured as IQ or, more
accurately, as g are both genetic and environmental in origin--just as are all
other psychological traits and attitudes studied so far, including
personality, vocational interests and societal attitudes. This is old news
among the experts. The experts have, however, been startled by more recent
discoveries.
One is that the heritability of IQ rises with age--that is to say, the extent
to which genetics accounts for differences in IQ among individuals increases
as people get older. Studies comparing identical and fraternal twins,
published in the past decade by a group led by Thomas J. Bouchard, Jr., of the
University of Minnesota and other scholars, show that about 40 percent of IQ
differences among preschoolers stems from genetic differences but that
heritability rises to 60 percent by adolescence and to 80 percent by late
adulthood. With age, differences among individuals in their developed
intelligence come to mirror more closely their genetic differences. It appears
that the effects of environment on intelligence fade rather than grow with
time. In hindsight, perhaps this should have come as no surprise. Young
children have the circumstances of their lives imposed on them by parents,
schools and other agents of society, but as people get older they become more
independent and tend to seek out the life niches that are most congenial to
their genetic proclivities.
A second big surprise for intelligence experts was the discovery that
environments shared by siblings have little to do with IQ. Many people still
mistakenly believe that social, psychological and economic differences among
families create lasting and marked differences in IQ. Behavioral geneticists
refer to such environmental effects as "shared" because they are common to
siblings who grow up together. Research has shown that although shared
environments do have a modest influence on IQ in childhood, their effects
dissipate by adolescence. The IQs of adopted children, for example, lose all
resemblance to those of their adoptive family members and become more like the
IQs of the biological parents they have never known. Such findings suggest
that siblings either do not share influential aspects of the rearing
environment or do not experience them in the same way. Much behavioral
genetics research currently focuses on the still mysterious processes by which
environments make members of a household less alike.
g on the Job
Although the evidence of genetic and physiological correlates of g argues
powerfully for the existence of global intelligence, it has not quelled the
critics of intelligence testing. These skeptics argue that even if such a
global entity exists, it has no intrinsic functional value and becomes
important only to the extent that people treat it as such: for example, by
using IQ scores to sort, label and assign students and employees. Such
concerns over the proper use of mental tests have prompted a great deal of
research in recent decades. This research shows that although IQ tests can
indeed be misused, they measure a capability that does in fact affect many
kinds of performance and many life outcomes, independent of the tests'
interpretations or applications. Moreover, the research shows that
intelligence tests measure the capability equally well for all native-born
English-speaking groups in the U.S.
If we consider that intelligence manifests itself in everyday life as the
ability to deal with complexity, then it is easy to see why it has great
functional or practical importance. Children, for example, are regularly
exposed to complex tasks once they begin school. Schooling requires above all
that students learn, solve problems and think abstractly. That IQ is quite a
good predictor of differences in educational achievement is therefore not
surprising. When scores on both IQ and standardized achievement tests in
different subjects are averaged over several years, the two averages correlate
as highly as different IQ tests from the same individual do. High-ability
students also master material at many times the rate of their low-ability
peers. Many investigations have helped quantify this discrepancy. For example,
a 1969 study done for the U.S. Army by the Human Resources Research Office
found that enlistees in the bottom fifth of the ability distribution required
two to six times as many teaching trials and prompts as did their
higher-ability peers to attain minimal proficiency in rifle assembly,
monitoring signals, combat plotting and other basic military tasks. Similarly,
in school settings the ratio of learning rates between "fast" and "slow"
students is typically five to one.
The scholarly content of many IQ tests and their strong correlations with
educational success can give the impression that g is only a narrow academic
ability. But general mental ability also predicts job performance, and in more
complex jobs it does so better than any other single personal trait, including
education and experience. The army's Project A, a seven-year study conducted
in the 1980s to improve the recruitment and training process, found that
general mental ability correlated strongly with both technical proficiency and
soldiering in the nine specialties studied, among them infantry, military
police and medical specialist. Research in the civilian sector has revealed
the same pattern. Furthermore, although the addition of personality traits
such as conscientiousness can help hone the prediction of job performance, the
inclusion of specific mental aptitudes such as verbal fluency or mathematical
skill rarely does. The predictive value of mental tests in the work arena
stems almost entirely from their measurement of g, and that value rises with
the complexity and prestige level of the job.
Half a century of military and civilian research has converged to draw a
portrait of occupational opportunity along the IQ continuum. Individuals in
the top 5 percent of the adult IQ distribution (above IQ 125) can essentially
train themselves, and few occupations are beyond their reach mentally. Persons
of average IQ (between 90 and 110) are not competitive for most professional
and executive-level work but are easily trained for the bulk of jobs in the
American economy. In contrast, adults in the bottom 5 percent of the IQ
distribution (below 75) are very difficult to train and are not competitive
for any occupation on the basis of ability. Serious problems in training
low-IQ military recruits during World War II led Congress to ban enlistment
from the lowest 10 percent (below 80) of the population, and no civilian
occupation in modern economies routinely recruits its workers from that range.
Current military enlistment standards exclude any individual whose IQ is below
about 85.
The importance of g in job performance, as in schooling, is related to
complexity. Occupations differ considerably in the complexity of their
demands, and as that complexity rises, higher g levels become a bigger asset
and lower g levels a bigger handicap. Similarly, everyday tasks and
environments also differ significantly in their cognitive complexity. The
degree to which a person's g level will come to bear on daily life depends on
how much novelty and ambiguity that person's everyday tasks and surroundings
present and how much continual learning, judgment and decision making they
require. As gamblers, employers and bankers know, even marginal differences in
rates of return will yield big gains--or losses--over time. Hence, even small
differences in g among people can exert large, cumulative influences across
social and economic life.
In my own work, I have tried to synthesize the many lines of research that
document the influence of IQ on life outcomes. As the illustration shows, the
odds of various kinds of achievement and social pathology change
systematically across the IQ continuum, from borderline mentally retarded
(below 70) to intellectually gifted (above 130). Even in comparisons of those
of somewhat below average (between 76 and 90) and somewhat above average
(between 111 and 125) IQs, the odds for outcomes having social consequence are
stacked against the less able. Young men somewhat below average in general
mental ability, for example, are more likely to be unemployed than men
somewhat above average. The lower-IQ woman is four times more likely to bear
illegitimate children than the higher-IQ woman; among mothers, she is eight
times more likely to become a chronic welfare recipient. People somewhat below
average are 88 times more likely to drop out of high school, seven times more
likely to be jailed and five times more likely as adults to live in poverty
than people of somewhat above-average IQ. Below-average individuals are 50
percent more likely to be divorced than those in the above-average category.
These odds diverge even more sharply for people with bigger gaps in IQ, and
the mechanisms by which IQ creates this divergence are not yet clearly
understood. But no other single trait or circumstance yet studied is so deeply
implicated in the nexus of bad social outcomes--poverty, welfare, illegitimacy
and educational failure--that entraps many low-IQ individuals and families.
Even the effects of family background pale in comparison with the influence of
IQ. As shown most recently by Charles Murray of the American Enterprise
Institute in Washington, D.C., the divergence in many outcomes associated with
IQ level is almost as wide among siblings from the same household as it is for
strangers of comparable IQ levels. And siblings differ a lot in IQ--on
average, by 12 points, compared with 17 for random strangers.
An IQ of 75 is perhaps the most important threshold in modern life. At that
level, a person's chances of mastering the elementary school curriculum are
only 50-50, and he or she will have a hard time functioning independently
without considerable social support. Individuals and families who are only
somewhat below average in IQ face risks of social pathology that, while lower,
are still significant enough to jeopardize their well-being. High-IQ
individuals may lack the resolve, character or good fortune to capitalize on
their intellectual capabilities, but socioeconomic success in the
postindustrial information age is theirs to lose.
What Is versus What Could Be
The foregoing findings on g's effects have been drawn from studies conducted
under a limited range of circumstances--namely, the social, economic and
political conditions prevailing now and in recent decades in developed
countries that allow considerable personal freedom. It is not clear whether
these findings apply to populations around the world, to the extremely
advantaged and disadvantaged in the developing world or, for that matter, to
people living under restrictive political regimes. No one knows what research
under different circumstances, in different eras or with different populations
might reveal.
But we do know that, wherever freedom and technology advance, life is an
uphill battle for people who are below average in proficiency at learning,
solving problems and mastering complexity. We also know that the trajectories
of mental development are not easily deflected. Individual IQ levels tend to
remain unchanged from adolescence onward, and despite strenuous efforts over
the past half a century, attempts to raise g permanently through adoption or
educational means have failed. If there is a reliable, ethical way to raise or
equalize levels of g, no one has found it.
Some investigators have suggested that biological interventions, such as
dietary supplements of vitamins, may be more effective than educational ones
in raising g levels. This approach is based in part on the assumption that
improved nutrition has caused the puzzling rise in average levels of both IQ
and height in the developed world during this century. Scientists are still
hotly debating whether the gains in IQ actually reflect a rise in g or are
caused instead by changes in less critical, specific mental skills. Whatever
the truth may be, the differences in mental ability among individuals remain,
and the conflict between equal opportunity and equal outcome persists. Only by
accepting these hard truths about intelligence will society find humane
solutions to the problems posed by the variations in general mental ability.
------------------------------------------------------------------------------
--
Useless hypotheses, etc.:
consciousness, phlogiston, philosophy, vitalism, mind, free will, qualia,
analog computing, cultural relativism, GAC, Cyc, Eliza, cryonics, individual
uniqueness, ego
Everything that can happen has already happened, not just once,
but an infinite number of times, and will continue to do so forever.
(Everything that can happen = more than anyone can imagine.)
We won't move into a better future until we debunk religiosity, the most
regressive force now operating in society.
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