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I.Q. (intelligence quotient)


(1916) A number used to express the appatent relative intelligence of a person, consisting of a ratio of the mental age (as reported on a standardized test) to the chronological age, multiplied by 100.[ IQ = (MA/CA)*100 ]

Scoring used for many standarized I.Q. tests:

average: 100
average range: 90-109

high average: 110-119
(above the bottom 75 percent and below the top 10 percent of the popultation)

superior: 120-129
(above the bottom 90 percent and below the top 2 percent of the population:

very superior: 130 and above
(the top 2 percent of the population)


Controversy follows psychological testing

Quantifying intellectual ability has emerged as one of the field's most hotly contested areas.

- APA (American Psychological Association) Monitor Online, VOLUME 30, NUMBER 11 December 1999

The concept of intelligence has existed for centuries, but it wasn't until this century that scientists began testing it--and debating the merits of doing so.

Intelligence testing was born of the study of individual differences, developed in the late 19th century. William Stern was perhaps most influential in founding a psychology of individual differences.

In 1897, France's Alfred Binet began work on tests of individual differences, which led him to study "subnormal" children in Paris schools. Several years later, Binet and Paris physician Theodore Simon recommended that an accurate diagnosis of intelligence be established for schoolchildren. The result was the Simon-Binet test of intelligence, which first appeared in 1905 and was revised in 1908.

Binet viewed the test as a tool for selecting students who needed special remedial teaching, not as a measure of absolute innate ability. The test was translated into English for the American audience in 1908 by Henry H. Goddard and gained great popularity.

Several revisions followed, but it was the 1916 revision by Lewis M. Terman in the form we still know as the Stanford-Binet test that would standardize the test. It was William Stern who believed that the test measured innate ability or limitation. These two views lie at the basis of much of the controversy over intelligence tests across this century.

In another significant development in tests, in 1911 William Stern contributed a formulation relating mental age to chronological age with his formulation of Intelligence Quotient. This simple formulation of IQ= MA/CA X 100 gave a number to stand for the performance of the child. This allowed the IQ to be manipulated within statistical tests and to be used for prediction of later performance.

During World War I, testing of military recruits provided the first massive use of psychological tests of intelligence. Robert M. Yerkes became the head of the Psychological Testing Corps during World War I. He and Terman helped develop the Army Alpha and Beta tests, which were used to screen soldiers during the war. Hundreds of psychologists and graduate students in psychology were recruited to administer the tests to recruits. The psychological test would be heavily engrained in American psychology thereafter.

After the war, the first major wave of criticism arose concerning psychological tests. One criticism had to do with the results of the Army test pertaining to race and nationality: The results indicated that southern and eastern Europeans were inferior to northern Europeans and that blacks were inferior to whites.

Carl Brigham's 1923 book "A Study of American Intelligence" supported those negative findings and increased the criticism of all forms of intelligence testing. Some modern critics have charged that the test results prompted restrictive emigration policies in America in 1924 and fanned the flames of racial prejudice against blacks and other minorities.

J. McKeen Cattell of Columbia was a promoter of psychological tests. In 1921, he founded the Psychological Corporation as a nonprofit publisher of psychological tests. It remains a major publisher, though now in the private sector.

David Wechsler developed his tests in response to many of the criticisms of the Binet tests. In 1939, he introduced his Wechsler Adult Intelligence Scale (WAIS), the first of a stable of tests still much in use. Since that time there have been many intelligence tests produced, some specifically aimed at reducing cultural and background effects on pencil-and-paper tests.

In 1969, the debate about the inherent versus the environmental bases of intelligence exploded with an article by Arthur Jensen in which he argued for the inheritance of racial differences in intelligence. The last decade of this century has also been caught up in a wave of contention in response to Herrnstein's and Murray's "The Bell Curve: Intelligence and Class Structure in American Life."

In recent years, influential books by R.J. Sternberg and Howard Gardner have supported multiple intelligences over a single global factor in intelligence. That debate is bound to continue.

Further reading:

Fancher, R.E. (1985). The intelligence men: makers of the IQ controversy. New York: Norton.

Minton, H.L. (1988). Lewis M. Terman: Pioneer in psychological testing. New York: New York University Press.

Sokal, M.M. (Ed.). (1987). Psychological testing and American society: 1890-1930. New Brunswick, NJ: Rutgers University Press.

Wolfe, T.H. (1973). Alfred Binet. Chicago: University of Chicago Press.



The Rising Curve [APA Book]
In this APA book, leading experts in psychology, sociology, psychometrics, and nutrition present and defend different interpretations of findings on the increase in intelligence test scores.

Preschoolers Seeking Novel Stimuli May Develop Higher IQ's
Toddlers who physically explore their environment, engage socially with other children and verbally interact with adults are likely to have better scholastic and reading abilities as teenagers compared to less engaging toddlers, according to a new study.

The higher the IQ, the less likelihood of PTSD, study suggests
APA Monitor article (April 2002) describing recent research findings that soldiers with higher IQs may be a lower risk of developing posttraumatic stress disorder.