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IQ classification is the practice by IQ test publishers of labeling IQ score ranges with (somewhat subjective) category names such as "superior" or "average".〔〔〔〔 There are several publishers of tests of cognitive abilities. No two publishers use exactly the same classification labels, which have changed from time to time since the beginning of intelligence testing in the early twentieth century. IQ scores have been derived by two different methods since the advent of cognitive ability tests. The first method historically was the "ratio IQ", based on estimating a "mental age" of the test-taker (rounded to a specified number of years and months), which was then divided by the test-taker's "chronological age" (rounded to a specified number of years and months). For example, a mental age score of thirteen years and zero months for a test-taker with the chronological age ten years and zero months results in a quotient of 1.3 after doing the division. The division result was then multiplied by 100 so that scores could be reported without decimal points. Thus the score in the example would be reported as IQ 130. The current scoring method for all IQ tests is the "deviation IQ". In this method, an IQ score of 100 means that the test-taker's performance on the test is at the median level of performance in the sample of test-takers of about the same age used to norm the test. An IQ score of 115 means performance one standard deviation above the median, a score of 85 performance one standard deviation below the median, and so on.〔 Lewis Terman and other early developers of IQ tests noticed that most child IQ scores come out to approximately the same number by either procedure. Deviation IQs are now used for standard scoring of all IQ tests in large part because they allow a consistent definition of IQ for both children and adults. By the current "deviation IQ" definition of IQ test standard scores, about two-thirds of all test-takers obtain scores from 85 to 115, and about 5 percent of the population scores above 125.〔 Historically, even before IQ tests were invented, there were attempts to classify people into intelligence categories by observing their behavior in daily life.〔〔 Those other forms of behavioral observation are still important for validating classifications based primarily on IQ test scores. Both intelligence classification by observation of behavior outside the testing room and classification by IQ testing depend on the definition of "intelligence" used in a particular case and on the reliability and error of estimation in the classification procedure. All IQ tests show variation in scores even when the same person takes the same test over and over again.〔〔 IQ scores also differ for a test-taker taking tests from more than one publisher at the same age.〔 The various test publishers do not use uniform names or definitions for IQ score classifications. All these issues must be kept in mind when interpreting an individual's IQ scores, because they all can result in different IQ classifications for the same person at different times. ==Variance in individual IQ classification== IQ tests generally are reliable enough that most people ages ten and older have similar IQ scores throughout life.〔 Still, some individuals score very differently when taking the same test at different times or when taking more than one kind of IQ test at the same age.〔 For example, many children in the famous longitudinal Genetic Studies of Genius begun in 1921 by Lewis Terman showed declines in IQ as they grew up. Terman recruited school pupils based on referrals from teachers, and gave them his Stanford–Binet IQ test. Children with an IQ above 140 by that test were included in the study. There were 643 children in the main study group. When the students who could be contacted again (503 students) were retested at high school age, they were found to have dropped 9 IQ points on average in Stanford–Binet IQ. More than two dozen children dropped by 15 IQ points and six by 25 points or more. Yet parents of those children thought that the children were still as bright as ever, or even brighter.〔 Because all IQ tests have error of measurement in the test-taker's IQ score, a test-giver should always inform the test-taker of the confidence interval around the score obtained on a given occasion of taking each test.〔 IQ scores are ordinal scores and are not expressed in an interval measurement unit.〔 Besides the inherent error band around any IQ test score because tests are a "sample of learned behavior", IQ scores can also be misleading because test-givers fail to follow standardized administration and scoring procedures. In cases of test-giver mistakes, the usual result is that tests are scored too leniently, giving the test-taker a higher IQ score than the test-taker's performance justifies. Some test-givers err by showing a "halo effect", with low-IQ individuals receiving IQ scores even lower than if standardized procedures were followed, while high-IQ individuals receive inflated IQ scores.〔 IQ classifications for individuals also vary because category labels for IQ score ranges are specific to each brand of test. The test publishers do not have a uniform practice of labeling IQ score ranges, nor do they have a consistent practice of dividing up IQ score ranges into categories of the same size or with the same boundary scores.〔 Thus psychologists should specify which test was given when reporting a test-taker's IQ.〔 Psychologists and IQ test authors recommend that psychologists adopt the terminology of each test publisher when reporting IQ score ranges.〔〔 IQ classifications from IQ testing are not the last word on how a test-taker will do in life, nor are they the only information to be considered for placement in school or job-training programs. There is still a dearth of information about how behavior differs between persons with differing IQ scores.〔 For placement in school programs, for medical diagnosis, and for career advising, factors other than IQ must also be part of an individual assessment. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「IQ classification」の詳細全文を読む スポンサード リンク
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