I.Q. n : a measure of a person's intelligence as indicated by an intelligence test; the ratio of a person's mental age to their chronological age (multiplied by 100) [syn: intelligence quotient, IQ]IQ n : a measure of a person's intelligence as indicated by an intelligence test; the ratio of a person's mental age to their chronological age (multiplied by 100) [syn: intelligence quotient, I.Q.]
An Intelligence Quotient or IQ is a score derived from one of several different standardized tests attempting to measure intelligence. The term "IQ," a translation of the German Intelligenz-Quotient, was coined by the German psychologist William Stern in 1912 as a proposed method of scoring early modern children's intelligence tests such as those developed by Alfred Binet and Theodore Simon in the early 20th Century. Although the term "IQ" is still in common use, the scoring of modern IQ tests such as the Wechsler Adult Intelligence Scale is now based on a projection of the subject's measured rank on the Gaussian bell curve with a center value (average IQ) of 100, and a standard deviation of 15 (different tests have various standard deviations; the Stanford-Binet IQ test has a standard deviation of 16).
IQ scores have been shown to correlate with such factors as morbidity and mortality, parental social status, and to a substantial degree, parental IQ: while IQ inheritance has been investigated for nearly a century, controversy remains as to how much is inheritable, and the mechanisms for inheriting are still a matter of some debate.
IQ scores are used in many contexts: as predictors of educational achievement or special needs, by social scientists who study the distribution of IQ scores in populations and the relationships between IQ score and other variables, and as predictors of job performance and income.
The average IQ scores for many populations were rising at an average rate of three points per decade during the 20th century with most of the increase in the lower half of the IQ range: a phenomenon called the Flynn effect. It is disputed whether these changes in scores reflect real changes in intellectual abilities, or merely methodological problems with past or present testing.
HistoryIn 1905 the French psychologist Alfred Binet published the first modern intelligence test, it was called the Binet-Simon intelligence scale. His principal goal was to identify students who needed special help in coping with the school curriculum. Along with his collaborator Theodore Simon, Binet published revisions of his intelligence scale in 1908 and 1911, the last appearing just before his untimely death.
In 1912, the German psychologist William Stern coined the abbreviation "I.Q.", a translation of the German Intelligenz-Quotient ("intelligence quotient"), proposing that an individual's intelligence level be measured as a quotient of their estimated "mental age" and their chronological age. A further refinement of the Binet-Simon scale was published in 1916 by Lewis M. Terman, from Stanford University, who incorporated Stern's proposal, and this Stanford-Binet Intelligence Scale formed the basis for one of the modern intelligence tests that remains in common use.
Originally, IQ was calculated as a ratio with the formula 100 \times \frac.
In 1939 David Wechsler published the first intelligence test explicitly designed for an adult population, the Wechsler Adult Intelligence Scale, or WAIS. Subsequent to the publication of the WAIS, Wechsler extended his scale for younger ages, creating the Wechsler Intelligence Scale for Children, or WISC. The Wechsler scales contained separate subscores for verbal and performance IQ, thus being less dependent on overall verbal ability than early versions of the Stanford-Binet scale, and was the first intelligence scale to base scores on a standardized normal distribution rather than an age-based quotient: since age-based quotients worked only for children, these methods were replaced by a projection of the measured rank on the Gaussian bell curve using an average IQ of 100 as the center value and a standard deviation of 15 or occasionally 16 or 24 points.
Thus, the modern IQ score is a mathematical transformation of a raw score on an IQ test, based on the rank of that score in a normalization sample, Modern scores are sometimes referred to as "deviance IQ", while older method age-specific scores are referred to as "ratio IQ".
The two methodologies yield similar results near the middle of the bell curve, but the older ratio IQs yielded far higher scores for the intellectually gifted— for example, Marilyn vos Savant, who appeared in the Guinness Book of World Records, obtained a ratio IQ of 228. While this score could make sense using Binet's formula (and even then, only for a child), on the Gaussian curve model it would be an exceptional 7.9 standard deviations above the mean and hence virtually impossible in a population with a normal IQ distribution (see normal distribution). In addition, IQ tests like the Wechsler were not intended to reliably discriminate much beyond IQ 130, as they simply do not contain enough exceptionally difficult items.http://www.minddisorders.com/Py-Z/Wechsler-Intelligence-Scale-for-Children.html
Since the publication of the WAIS, almost all intelligence scales have adopted the normal distribution method of scoring. The use of the normal distribution scoring method makes the term "intelligence quotient" an inaccurate description of the intelligence measurement, but "I.Q." still enjoys colloquial usage, and is used to describe all of the intelligence scales currently in use.
StructureIQ tests come in many forms, and some tests use a single type of item or question, while others use several different subtests. Most tests yield both an overall score and individual subtest scores.
A typical IQ test requires the test subject to solve a fair number of problems in a set time under supervision. Most IQ tests include items from various domains, such as short-term memory, verbal knowledge, spatial visualization, and perceptual speed. Some tests have a total time limit, others have a time limit for each group of problems, and there are a few untimed, unsupervised tests, typically geared to measuring high intelligence. One test for determining IQ is the WAIS (Wechsler Adult Intelligence Scale-Third Edition). The WAIS-III consists of fourteen subtests, seven verbal (Information, Comprehension, Arithmetic, Similarities, Vocabulary, Digit Span, and Letter-Number Sequencing) and seven performance (Digit Symbol-Coding, Picture Completion, Block Design, Matrix Reasoning, Picture Arrangement, Symbol Search, and Object Assembly).
Pearson Education, Inc., the publisher of the Wechsler Intelligence Scale, has announced that the next version, the WAIS-IV, is to be released in 2008.http://www.wais-iv.com
When standardizing an IQ test, a representative sample of the population is tested using each test question.The sample is then divided by the mean score. IQ tests are calibrated in such a way as to yield a normal distribution, or "bell curve". Each IQ test, however, is designed and valid only for a certain IQ range. Because so few people score in the extreme ranges, IQ tests usually cannot accurately measure very low and very high IQs.
Various IQ tests measure a standard deviation with a different number of points. Thus, when an IQ score is stated, the standard deviation used should also be stated.
When an individual has scores that do not correlate with each other, there is a good reason to suspect a learning disability or other cause for this lack of correlation. Tests have been chosen for inclusion because they display the ability to use this method to predict later difficulties in learning.
An individual's IQ score may or may not be stable over the course of the individual's lifetime.
Grade range percent(with a standard deviation of 15)
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