Intelligence Quotient (IQ)

A measurement of intelligence based on performance on intelligence tests. Use of intelligence testing remains controversial because of the limitations of testing for specific abilities and knowledge, and because of possible cultural bias in the design of tests.

Nonetheless, intelligence quotient (IQ) is used in educational and psychological settings in combination with other types of tests in order to evaluate a child’s mental capacity and to recommend appropriate remediation or treatment.

For children with learning disabilities, IQ scores can demonstrate superior intelligence despite weak language skills or poor academic performance. Conversely, poor performance on intelligence tests can inaccurately reflect true ability and potential, with many capable individuals outperforming the level of achievement their IQ scores might have predicted.

IQ is generally based on a mean of 100, with scores ranging in classification from “mentally retarded” at the low end to “very superior” at the high end.

The concept of intelligence has existed for centuries, but it was not until this century that scientists began testing it and debating whether or not they should. Intelligence testing was developed in the late 19th century as 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 thought of 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 revised several times, but it was not until 1916 that the test was standardized with the revision by Lewis M. Terman in the form still known as the Stanford-Binet test.

In 1911 William Stern developed the idea of relating mental age to chronological age with his formulation of Intelligence Quotient. This simple formulation of IQ= MA/CA × 100 gave a number that would 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 the first massive use of psychological tests of intelligence was begun with the testing of military recruits. Hundreds of psychologists and graduate students in psychology were recruited to administer the tests to recruits. After the war critics were outraged to find that the Army test suggested that southern and eastern Europeans were inferior to northern Europeans, and that blacks were inferior to whites. Some believe it was these test results that prompted restrictive emigration policies in America in 1924 and fanned the flames of racial prejudice against blacks and other minorities.

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 penciland- paper tests. In 1969 the debate about the inherent versus the environmental bases of intelligence exploded with an article by psychologist Arthur Jensen in which he argued for the inheritance of racial differences in intelligence. The debate continued into the last decade of the 20th century in response to further controversial work on intelligence and class structure in American life. In recent years influential books by psychologist Howard Gardner and others have supported the idea of multiple intelligences over a single global factor in intelligence.