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About IQ
The term ‘intelligence quotient’ was first coined in 1912 by German psychologist, William Stern in reference to the intelligence tests developed by psychologists Alfred Binet and Theodore Simon, who wanted to identify students that needed special help with the school curriculum. The original formula for calculating IQ was:
(mental age divided by chronological age) x 100
In other words, a person’s intelligence level was measured as a quotient of their estimated mental age and chronological age. A 10-year-old child that had the mental age of a 12-year-old was considered to have an above average IQ of 120 [(12/10) x 100].
In the 1930’s an intelligence test explicitly for adults was designed by American psychologist, David Wechsler, called the Wechsler Adult Intelligence Scale (WAIS). This was followed by the Wechsler Intelligence Scale for Children (WISC). These scales differed from the earlier versions by basing the scores on a standardised normal distribution rather than on an age-based quotient, because the latter only worked for children.
Using the newer method, an average IQ of 100 was set as the centre value on a ‘bell curve’, with a standard deviation of 15 points and each score was “ranked” by a projection on the normal distribution.
Most modern intelligence scales are now based on the normal distribution method of scoring and in effect, makes the term “intelligence quotient” inaccurate but the term is now widely accepted and therefore retains colloquial usage.
Flynn Effect
The Flynn effect describes an increase in the average intelligence quotient (IQ) test scores over generations (IQ gains over time). Similar impro- vements have been reported for other cognitions such as semantic and episodic memory. The effect has been observed in most parts of the world at different rates.
The Flynn effect is named for James R. Flynn, who did much to document it and promote awareness of its implications. The term itself was coined by the authors of The Bell Curve.
The effect increase has been continuous and approximately linear from the earliest years of testing to the present. "Test scores are certainly going up all over the world, but whether intelligence itself has risen remains controversial," psychologist Ulric Neisser wrote in an article during 1997 in The American Scientist.
The Flynn effect may have ended in some developed nations starting during the mid 1990s although other studies, such as Black Americans reduce the racial IQ gap: Evidence from standardization samples (Dickens, Flynn; 2006), still show gains between 1972 and 2002.
IQ tests are re-normalized periodically, in order to maintain an average score at 100. In fact, the necessity of this re-normalization provided an early indication that IQ was changing over time. The revised versions are standardized on new samples and scored with respect to those samples alone, so the only way to compare the difficulty of two versions of a test is to conduct a separate study in which the same subjects take both versions.
The average rate of increase seems to be about three IQ points per decade. Because children attend school longer now and have become much more familiar with the testing of school-related material, one might expect the greatest gains to occur on such school content-related tests as vocabulary, arithmetic or general information. Just the opposite is the case: abilities such as these have experienced relatively small gains and even occasional decreases over the years. The greatest Flynn effects occur instead for general intelligence factor loaded (g-loaded) tests such as Raven's Progressive Matrices. For example, Dutch conscripts gained 21 points during only 30 years, or 7 points per decade, between 1952 and 1982.
Some studies emphasizing the distribution of scores have found the Flynn effect to be primarily a phenomenon of the lower end of the distribution. Teasdale and Owen (1987),
Source: Wikipedia
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