Henry Goddard: administered intelligence tests to arriving immigrants and concluded
certain races were “feebleminded”, resulting in the sterilization of “mental defectives”.
Alfred Binet and Theodrore Simon: developed the first intelligence test to identify children
who needed remedial education by measuring their aptitude for learning independent of the
child’s prior educational achievement. This was a test of natural intelligence.
William Stern suggested that this mental level produced by the intelligence test could be
understood as a child’s mental age.
Lewis Terman formalized this with the development of the intelligence quotient/ratio IQ,
which is IQ= (mental age/chronological age)x100. Due to anomalies with the intelligence
quotient, psychologists devised the deviation IQ= (person’s test core/average test core of
people in the same age group)x100. This was then plotted on a normal curve.
Two commonly used tests are the Stanford-Binet (updated many times from the original,
most notably by Lewis Terman) and the WAIS (the Wechsler Adult Intelligence Scale). The
WAIS test yields a verbal score, a performance score, as well as an overall score of
intelligence. However, the 13 WAIS tests do not require written words.
- Intelligence scores only become stable after about 7 years of age
- Measure responses that are known to be correlated with consequential behaviors
that are thought to be made possible by intelligence
- Test scores predict a person’s academic performance, job performance, health,
wealth, attitudes, and even basic cognitive abilities
Charles Spearman, a student of Wilhelm Wundt (who founded the first experimental
psychology laboratory) invented a technique known as factor analysis- a statistical
technique that explains a large number of correlations in terms of a small number of
underlying factors. He believed that if intelligence is a single, general ability, then there
should be a very strong positive correlation between people’s performances on all kinds of
tests. His experiment shown that different measures were positively correlated but not
perfectly correlated: the child who had the highest score on one measure didn’t necessarily
have the highest score on every measure. Thus, he developed the two-factor theory of
intelligence, which suggested that every task requires a combination of a general ability (g)
and skills that are specific to the task (s).
Louis Thurstone argued that there was no “general ability (g)”. Instead, there were few
stable and independent mental abilities such as perceptual, verbal, and numerical ability,
which he called the primary mental abilities.
Confirmatory factor analysis solved the question of “intelligence”. It is a hierarchy, with a
general intelligence (g) at the top, specific factors (s) at the bottom, and a set of group factors
(primary mental abilities) in the middle.
People who score well on one test of mental ability usually score well on others, which
suggest that there is a property called g (general intelligence). People who score well on one
test of mental ability don’t always score well on others, which suggest there is s (specific
abilities). In between g and s, there are several middle-level abilities. Data-Based Approach
- Suggests that there are 8 middle-level abilities
John Caroll found the pattern of correlations among these tests suggested the existence of 8
independent middle-level abilities: memory and learn