American education » Intelligence quotient

Published: 4-07-2011, 10:02

Intelligence quotient

A measure of an individual’s “general ability” compared to others of the same age. First used with the 1916 version of the STANFORD-BINET INTELLIGENCE TESTS, the I.Q. score originated in 1908, when French psychologist Alfred Binet developed the concept of “mental age.” The intelligence quotient was derived by dividing the raw score on the Stanford-Binet test—the so-called mental age—by the test-taker’s chronological age and then multiplying by 100. The mean I.Q. of 100 is the result of dividing a mental age by an equivalent chronological age. A 12-year-old child with a mental age of 12 has an I.Q. of 100. A mental-age measurement of 12 produces an I.Q. of 120 for a 10-year-old and an I.Q. of 80 for a 15-year-old. Intelligence quotients can be derived from any of a wide variety of standardized intelligence tests, all of which are designed for specific age groups because of the changing nature of mental age.
Sometimes called intellectual age, the mental age is, at best, a vague concept. It tends to accelerate during early childhood and decelerate— indeed, even shrink—during adulthood. Thus, children with identical mental and chronological ages, and, therefore, I.Q.s of 100 on their third birthday may see their mental ages reach 12 by their 10th birthday, settle back to 30 on their 30th birthday and decline to 48 by the time they reach 50. Properly designed I.Q. tests should in theory produce consistent intelligence quotients of 100 throughout their lives, assuming, as do many psychologists, that I.Q. is a genetically determined attribute unaffected by environment. In fact, I.Q. scores can vary dramatically during an individual’s lifetime— usually as a function of the individual’s cultural environment, but often because of the type of test. Indeed, studies at Yale University’s Institute of Human Relations in the 1950s showed that the I.Q.s of identical twins did not remain identical when the twins were separated at birth and adopted into different homes. The I.Q.s of some of the children varied as much as 20% from those of their twin siblings during their first 10 years—always in apparent reflection of the cultural level of their adoptive homes.
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