|Alfred Binet: Along
with Theodore Simon developed the first intelligence test in France in
1904. It was designed to measure a child's mental age in
order to predict future school performance. The test was called
the Simon-Binet Intelligence Test. It was later revised at
Stanford University by Lewis Terman and is now known today as the
Intelligence Quotient (IQ): defined originally (Stern) as the ratio
of mental age (MA) to chronological age (CA) multiplied by 100 (thus, IQ
= MA/CA * 100). On contemporary intelligence tests, the average
performance for a given age is assigned a score of 100.
Wechsler Adult Intelligence Scale (WAIS) & Wechsler Intelligence
Scale for Children (WISC): These are the 2 most frequently
used IQ tests in the US. They provide a verbal IQ along
with a non-verbal or performance IQ. They also provide an
overall or full-scale IQ score. The Wechsler tests have a
mean of 100 and a standard deviation of 15.
Principles of Test Construction
Standardization: defining meaningful scores by comparison with
the performance of a pretested "standardization group".
Normal Curve: the symmetrical
bell-shaped curve that describes the distribution of many physical and
psychological traits (including intelligence). Most scores fall near the
average, and fewer and fewer scores lie near the extremes.
Reliability: the extent to which a test yields consistent
results, as assessed by the consistency of scores on two halves of the
test (split-half reliability) or on retesting at a later date
Validity: the extent to which a test measures or predicts what it
is supposed to.
a) Face Validity: the extent
to which questions on a test appear to measure the construct of
b) Content Validity: extent to
which a test actually measures the construct of interest.
c) Predictive Validity: the
success with which a test predicts the behavior it is designed to
predict. This is assessed by computing the correlation between
|test scores and the
criterion behavior (also called criterion-related validity).
Criterion: the behavior (such as college grades) that a test
(such as the SAT) is designed to predict.
Extremes of Intelligence
Mental Retardation: a condition of limited mental ability,
indicated by an IQ score below 70 and difficulty in adapting to the
demands of life; varies from mild to profound.
Down Syndrome: a condition of retardation and associated physical
disorders caused by an extra chromosome in one's genetic makeup.
Heritability: the proportion of variation among individuals on a
particular trait that can attributed to the differences in their genes.
Twin & adoption studies show that genetics do play a role in
intelligence (e.g., IQ's of identical twins correlate at about .85,
while fraternal twins at about .60).
However, the same studies show
how important environment is in that identical twins reared together
correlate at .85, while those raised in different homes correlate at
Most psychologist agree that differences in group IQ scores based on
ethnic background or gender are due to environmental differences not