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IQ Score Interpretation |
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IQ
scores are often misunderstood. Learn the basics of IQ score
interpretation in this article. |
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Intelligence testing began in earnest in France, when in
1904 psychologist Alfred Binet was commissioned by the French
government to find a method to differentiate between children who
were intellectually normal and those who were inferior. The purpose
was to put the latter into special schools. There they would receive
more individual attention and the disruption they caused in the
education of intellectually normal children could be
avoided.
This
led to the development of the Binet Scale, also known as the
Simon-Binet Scale in recognition of Theophile Simon's
assistance in its development. The test had children do tasks such
as follow commands, copy patterns, name objects, and put things in
order or arrange them properly. Binet gave the test to Paris
schoolchildren and created a standard based on his data. Following
Binet’s work, the phrase “intelligence quotient,” or “IQ,” entered
the vocabulary.
Lewis M. Terman worked on revising the Simon-Binet
Scale. His final product, published in 1916 as the Stanford
Revision of the Binet-Simon Scale of Intelligence (also known as
the Stanford-Binet), became the standard intelligence test in
the United States for the next several decades. By the 1920s mass
use of the Stanford-Binet Scale and other tests had created a
multimillion-dollar testing industry.
Despite the fact that the IQ test industry is already a
century old, IQ scores are still often misunderstood. Comments like,
“What do you mean my child isn’t gifted — he got 99 on those tests!
That’s nearly a perfect score, isn’t it?” or “The criteria you
handed out says ‘a score in the 97th percentile or above.’ Susan got
an IQ score of 97! That meets the requirement, doesn’t it?” are not
unusual and indicate a complete misunderstanding of IQ
scores. |
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Understanding IQ Scores |
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IQ
stands for intelligence quotient. Supposedly, it is a score that
tells one how “bright” a person is compared to other people. The
average IQ is by definition 100; scores above 100 indicate a higher
than average IQ and scores below 100 indicate a lower that average
IQ. Theoretically, scores can range any amount below or above 100,
but in practice they do not meaningfully go much below 50 or above
150.
Half
of the population have IQ’s of between 90 and 110, while 25% have
higher IQ’s and 25% have lower IQ’s:
Descriptive
Classifications of Intelligence Quotients |
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IQ |
Description |
% of
Population |
130+ |
Very
superior |
2.2% |
120-129 |
Superior |
6.7% |
110-119 |
High average |
16.1% |
90-109 |
Average |
50% |
80-89 |
Low average |
16.1% |
70-79 |
Borderline |
6.7% |
Below 70 |
Extremely
low |
2.2% |
Apparently, the IQ
gives a good indication of the occupational group that a person will
end up in, though not of course the specific occupation. In their
book, Know Your Child’s IQ, Glen Wilson and Diana Grylls
outline occupations typical of various IQ levels:
140 |
Top Civil Servants;
Professors and Research Scientists. |
130 |
Physicians and Surgeons;
Lawyers; Engineers (Civil and Mechanical) |
120 |
School Teachers;
Pharmacists; Accountants; Nurses; Stenographers;
Managers. |
110 |
Foremen; Clerks; Telephone
Operators; Salesmen; Policemen; Electricians. |
100+ |
Machine Operators;
Shopkeepers; Butchers; Welders; Sheet Metal
Workers. |
100- |
Warehousemen; Carpenters;
Cooks and Bakers; Small Farmers; Truck and Van
Drivers. |
90 |
Laborers; Gardeners;
Upholsterers; Farmhands; Miners; Factory Packers and
Sorters. | |
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IQ Expressed in
Percentiles |
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IQ
is often expressed in percentiles, which is not the same as
percentage scores, and a common reason for the misunderstanding of
IQ scores. Percentage refers to the number of items which a child
answers correctly compared to the total number of items presented.
If a child answers 25 questions correctly on a 50 question test he
would earn a percentage score of 50. If he answers 40 questions on
the same test his percentage score would be 80. Percentile, however,
refers to the number of other test takers’ scores that an
individual’s score equals or exceeds. If a child answered 25
questions and did better than 50% of the children taking the test he
would score at the 50th percentile. However, if he answered 40
questions on the 50 item test and everyone else answered more than
he did, he would fall at a very low percentile — even though he
answered 80% of the questions correctly.
On
most standardized tests, an IQ of 100 is at the 50th percentile.
Most of our IQ tests are standardized with a mean score of 100 and a
standard deviation of 15. What that means is that the following IQ
scores will be roughly equivalent to the following
percentiles:
IQ |
Percentile |
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65 |
01 |
70 |
02 |
75 |
05 |
80 |
09 |
85 |
16 |
90 |
25 |
95 |
37 |
100 |
50 |
105 |
63 |
110 |
75 |
115 |
84 |
120 |
91 |
125 |
95 |
130 |
98 |
135 |
99 |
An
IQ of 120 therefore implies that the testee is brighter than about
91% of the population, while 130 puts a person ahead of 98% of
people. A person with an IQ of 80 is brighter than only 9% of
people, and only a few score less than 60. |
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Be
Cautious! |
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It
is necessary to be very cautious in using a descriptive
classification of IQ’s. The IQ is, at best, a rough measure of
academic intelligence. It certainly would be unscientific to
say that an individual with an IQ of 110 is of high average
intelligence, while an individual with an IQ of 109 is of only
average intelligence. Such a strict classification of intellectual
abilities would fail to take account of social elements such as
home, school, and community. These elements are not adequately
measured by present intelligence tests. Furthermore, it would not
take account of the fact that an individual may vary in his test
score from one test to another.
Measures of intelligence may be valuable — although the
value is often overrated — but much harm can be done by persons who
try to classify individuals strictly on the basis of such measures
alone. No one should be either alarmed or discouraged if he finds
that his IQ is not as high as he might have hoped. Remember that
many elements besides IQ contribute to success and happiness. Also
note that IQ is not a fixed quantity, but can be increased by means
of education. This was demonstrated by the Milwaukee project as well
as numerous other research studies. |
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The Milwaukee
Project |
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In
the late 1960s, under the supervision of Rick Heber of the
University of Wisconsin, a project was begun to study the effects of
intellectual stimulation on children from deprived environments. In
order to find a “deprived environment” from which to draw
appropriate subjects for the study, Heber and his colleagues
examined the statistics of different districts within the city of
Milwaukee. One district in particular stood out. The residents of
this district had the lowest median income and lowest level of
education to be found in the city. This district also had the
highest population density and rate of unemployment of any area of
Milwaukee. There was one more statistic that really attracted
Heber’s attention: Although this district contained only 3 percent
of the city’s population, it accounted for 33 percent of the
children in Milwaukee who had been labeled “mentally
retarded”!
At
the beginning of the project, Heber selected forty newborns from the
depressed area of Milwaukee he had chosen. The mothers of the
infants selected all had IQ’s below 80. As it turned out, all of the
children in the study were black, and in many cases the fathers were
absent. The forty newborns were randomly assigned, 20 to an
experimental group and 20 to a control group.
Both
the experimental group and the control group were tested an equal
number of times throughout the project. An independent testing
service was used in order to eliminate possible biases on the part
of the project members. In terms of physical or medical variables,
there were no observable differences between the two
groups.
The
experimental group entered a special program. Mothers of the
experimental group children received education, vocational
rehabilitation, and training in homemaking and child care. The
children themselves received personalized enrichment in their home
environments for the first three months of their lives, and then
their training continued at a special center, five days a week,
seven hours a day, until they were ready to begin first grade. The
program at the center focused upon developing the language and
cognitive skills of the experimental group children. The control
group did not receive special education or home-based intervention
and enrichment.
By
the age of six all the children in the experimental group were
dramatically superior to the children in the control group. This was
true on all test measures, especially those dealing with language
skills or problem solving. The experimental group had an IQ average
of 120.7 as compared with the control group’s 87.2!
At
the age of six the children left the center to attend the local
school. By the time both groups were ten years old and in fifth
grade, the IQ scores of the children in the experimental group had
decreased to an average of 105 while the control group’s average
score held steady at about 85. One possible reason for the decline
is that schooling was geared for the slower students. The brighter
children were not given materials suitable for their abilities and
they began to fall back. Also, while the experimental children were
in the special project center for the first six years they ate well,
receiving three hot, balanced meals a day. Once they left the center
and began to attend the local school, many reported going to classes
hungry, without breakfast or a hot lunch. |
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Sources: |
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- Dworetzky, J. P.,
Introduction to Child Development (St. Paul: West
Publishing Company, 1981).
- Engle, T. L., &
Snellgrove, L., Psychology: Its Principles and Applications
(6th ed.), (Harcourt Brace Jovanovich, Inc.: New York, 1974).
- Swiegers, D. J., & Louw,
D. A., “Intelligensie,” in D. A. Louw (ed.), Inleiding tot die
Psigologie (2nd ed.), (Johannesburg: McGraw Hill, 1982).
- “Test Score Interpretation,”
Hampton City Schools, Psychological Services.
- Wilson, G., & Grylls, D.,
Know Your Child’s IQ (Futura Publications: London, 1977).
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