Background
The Board of Scientific Affairs (BSA) of the APA had concluded that after the publication of The Bell Curve
(1994) and the following debate that there were "serious
misunderstandings" and "that there was urgent need for an authoritative
report on these issues—one that all sides could use as a basis for
discussion". Furthermore, "Another unfortunate aspect of the debate was
that many participants made little effort to distinguish scientific
issues from political ones, Research findings were often assessed not so
much on their merits or their scientific standing as on their supposed
political implications." The report stated that "The charge to our Task
Force was to prepare a dispassionate survey of the state of the art: to
make clear what has been scientifically established, what is presently
in dispute, and what is still unknown. In fulfilling that charge, the
only recommendations we shall make are for further research and calmer
debate."
It was published on August 7, 1995. It was authored by a task
force of 11 experts. The APA Board on the Advancement of Psychology in
the Public Interest (BAPPI) nominated one member of the Task Force. The
Committee on Psychological Tests and Assessment nominated another. A
third was nominated by the Council of Representatives. The other members
were chosen by an extended consultative process with the aim of
representing a broad range of expertise and opinion. Ulric Neisser was appointed Chair. Three of the experts were also among the 52 signatories to "Mainstream Science on Intelligence",
an editorial published in 1994. Members of BSA and BAPPI were asked to
comment on a preliminary draft of the report. The entire Task Force gave
unanimous support to the final report. An edited version of Intelligence: Knowns and Unknowns was published in the journal American Psychologist in February 1996.
Findings
Intelligence: Knowns and Unknowns stated that many different theories of intelligence have been proposed. Many questions were still unanswered.
General intelligence factor
Most research had been done on psychometric testing which was also by far the most widely used in practical settings. Intelligence quotient (IQ) tests do correlate with one another and that the view that the general intelligence factor (g)
is a statistical artifact is a minority one. IQ scores are fairly
stable during development in the sense that while a child's reasoning
ability increases, the child's relative ranking in comparison to that of
other individuals of the same age is fairly stable during development.
IQ correlation with skills and grades
The
report stated that IQ scores measure important skills as they correlate
fairly well (0.5) with grades. This implied that the explained variance
(given certain linear assumptions) is 25%. "Wherever it has been
studied, children with high scores on tests of intelligence tend to
learn more of what is taught in school than their lower-scoring peers.
There may be styles of teaching and methods of instruction that will
decrease or increase this correlation, but none that consistently
eliminates it has yet been found."
IQ correlation with school achievement tests
IQ
scores also correlated with school achievement tests designed to
measure knowledge of the curriculum. Other personal characteristics
affecting this may be persistence, interest in school, and willingness
to study which may be influenced by the degree of encouragement for
academic achievement a child receives and more general cultural factors.
Test scores were the best single predictor of an individual's years of
education. They were somewhat more important than social class as
measured by occupation/education of parents.
IQ correlation with measures of job performance
IQ
scores were also correlated (0.3–0.5) with various measures of job
performance such as supervisor ratings and work samples. The
correlations were higher when the unreliability of such measures were
controlled for. IQ scores were sometimes described as the "best
available predictor" of job performance. Intelligence test scores did
correlate significantly with social status and income later in life.
They were somewhat less important for this than parental SES although
the effects of parental SES and IQ were hard to separate. IQ tests had
lower negative correlations with certain socially undesirable outcomes
such as that children with high IQ were less likely to engage in
juvenile crime. One example being a study finding a correlation of −0.19
(−0.17 with social class controlled for) between IQ scores and number
of juvenile offenses in a large Danish sample. This implied that the explained variance (given certain linear assumptions) is less than 4% for these negative outcomes.
Genetic and environmental variables
While
both genetic and environmental variables were involved in the
manifestation of intelligence, the role of genetics had been shown to
increase in importance with age. In particular, the effect of the family
environment shared by all children in a family, while important in
early childhood, became quite small (zero in some studies) by late
adolescence. Why this occurs is unclear. One possibility is that people
with different genes tend to seek out different environments that
reinforce the effects of those genes. Nonetheless, there were several
important environmental factors which were known to affect IQ, such as
having received very poor or interrupted schooling.
Interventions
However, regarding interventions such as the Head Start Program
and similar programs lasting one or two years, while producing initial
IQ gains, these had disappeared by the end of elementary school,
although there may be other benefits such as more likely to finish high
school. The more intensive Abecedarian Project had produced more long-lasting gains.
Other biological factors
The
report stated that a number of biological factors, including
malnutrition, exposure to toxic substances, and various prenatal and
perinatal factors, resulted in lowered IQ under at least some
conditions. The much-discussed "Flynn effect",
which refers to the striking worldwide mean IQ increase over time,
seemed too large to have simply reflected increased test sophistication.
Possible explanations included improved nutrition and more complex
environment. It was also unclear to what degree the IQ increase
reflected real gain in intelligence.
Group differences
The
report states that group differences in intelligence continue to be the
subject of intense interest and debate. Reasons include social,
psychological, political, and legal. The report states that "the facts
about group differences may be relevant to the need for (and the
effectiveness of) affirmative action programs". However, the report
specifically states that it does not make any policy recommendations.
Regarding sex differences so have most standard tests of
intelligence been constructed to show equal results, but some studies
show small differences. Males do better on visual-spatial tasks, with a
particularly large difference on mental rotation (nearly 1 SD), which is
significant for their generally better performance in tasks that
involve aiming and throwing. Males also do relatively better on tests of
proportional and mechanical reasoning as well as on mathematics.
Females do better on verbal tests and some memory tests. They do
relatively better in tests of literature, English composition, Spanish,
reading, and spelling. More males have dyslexia and stuttering. Possible
causes include gender roles and differences in brain structure which in
turn may be due to genetics and/or environment. Differences in sex
hormones may be another explanation. Female exposure to high levels of
male hormones in utero
is associated with higher spatial abilities and with more play with
"boys' toys" and less with 'girls' toys". Males with higher testosterone
levels do better on visuo-spatial abilities and worse on verbal
abilities. Older males given testosterone score better on visuo-spatial
tests.
As the measured differences in average intelligence between
various ethnic groups reflect complex patterns, no overall
generalization about them was appropriate. Regarding Asian Americans,
studies had shown slightly lower to slightly higher scores compared to
White Americans. Average IQ in East Asian nations had been reported as
equal to or substantially above the American average. Asians did
particularly well on spatial tests. Their knowledge of mathematics were
above that predicted from IQ scores which may reflect cultural
differences or higher spatial ability. Their occupational achievement
were also higher than predicted by IQ scores, with Asians with IQs
slightly below 100 having occupational achievements typically seen in
persons with IQs from 110 to 120. According to the report, "These
'over-achievements' serve as sharp reminders of the limitations
of IQ-based prediction." In addition to cultural factors, gene-based temperamental factor may also have been important.
Hispanics
scores typically were between those of Blacks and Whites. Linguistic
factors may have been particularly important for this group with many
not speaking English well or English not their first language. This may
have been reflected in higher scores on performance than on verbal
subtests. Nevertheless, for young children the WISC-R had reasonably
high correlations with school achievement measures. Standard aptitude
tests predicted first-year college grades about as well for Hispanic
high school students with moderate to high English proficiency as they
did for non Hispanic Whites.
Native Americans
were culturally and linguistically diverse as well as living in widely
varying settings. Groups, like the Inuit, who lived in the arctic tended
to do particularly well, with no substantial sex difference, on
visual-spatial skills. This likely represented a genetic and/or learned
adoption to the difficult arctic environment. Many Indian children
suffered from chronic middle-ear infection and hearing loss can have
marked negative effects on verbal tests. This may have been related to
the relatively lower verbal scores for this group.
There was a long-standing 15 point or 1 standard deviation difference between the intelligence test scores of African Americans and White Americans,
though it might have narrowed slightly in the then recent years. The
difference was largest on those tests, verbal or non-verbal, that best
represented the general intelligence factor (g).
Controlled studies of the way the tests were formulated and
administered had shown that this did not contribute substantially to the
difference. Attempts to devise tests that would minimize disadvantages
of this kind had been unsuccessful. The scores predicted future
achievement equally well for Blacks and Whites. "The cause of that
differential is not known; it is apparently not due to any simple form
of bias in the content or administration of the tests themselves. The
Flynn effect shows that environmental factors can produce differences of
at least this magnitude, but that effect is mysterious in its own
right. Several culturally based explanations of the Black/White IQ
differential have been proposed; some are plausible, but so far none has
been conclusively supported. There is even less empirical support for a
genetic interpretation. In short, no adequate explanation of the
differential between the IQ means of Blacks and Whites is presently
available."
Members of the task force
* = Mainstream Science on Intelligence signatory
Reception
In 2002, senior editor of Skeptic magazine Frank Miele interviewed psychologist Arthur Jensen
about the public and academic reception of his work and how he
interpreted the APA task force's summary dismissal of one of the main
tenets of Jensen's own position, i.e. that genetics play a significant
role in the appearance of between-group differences in IQ. Jensen
responded:
As I read the APA statement, [...] I didn't feel it was contradicting my position, but rather merely sidestepping it. It seems more evasive of my position than contradictory. The committee did acknowledge the factual status of what I have termed the Spearman Effect, the reality of g, the inadequacy of test bias and socioeconomic status as causal explanations, and many other conclusions that don't differ at all from my own position. [...] Considering that the report was commissioned by the APA, I was surprised it went as far as it did. Viewed in that light, I am not especially displeased by it.
