Short for an intelligence quotient test, an IQ test measures a person's cognitive ability compared to the population at large. It's a standardized test, and 100 is the median, or average, score. That means a person with an IQ within 10 points or so of 100 is of average intelligence compared to the rest of the population. A person whose score is below 70 may have developmental delays related to intelligence and a person whose score is above 130 is typically exceptionally smart.
A IQ test is not something for which a person can study. It test does not measure the quantity of your knowledge but rather measures a person's general intellectual ability to understand ideas, as compared to the general population at the same developmental level. How well we reason, distinguish relationships and solve problems are the kinds of things the test aims to discern. An IQ test also measures how well we process information, particularly our ability to store and retrieve it. Except in extreme circumstances, such as diseases that affect the brain, a person's IQ tends to stay about the same throughout life.
While IQ tests can be quite predictive of general intelligence, it's important to remember that they don't purport to tell the whole story of a person's abilities. Things an IQ test doesn't measure include creativity, emotional sensitivity, social competence, various acquired skills and many other things that usually fall under the general heading of intelligence. So a person who displays exceptional creativity, for example, may only manage an average IQ test score.
Among the more well known IQ tests are the Stanford-Binet, the Woodcock-Johnson Tests of Cognitive Abilities, the Wechsler Adult Intelligence Scale and the Wechsler Intelligence Scale for Children. The roots of the IQ tests of today trace back to one of the namesakes on that list. French researcher Alfred Binet devised what came to be known as the Binet-Simon Scale, which looked at tasks that could measure children's abilities across several age ranges [source: Indiana University].
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