Besides the reported error interval around IQ test scores, an IQ score could be misleading if a test-giver failed to follow standardized administration and scoring procedures. IQ scores are ordinal scores and are not expressed in an interval measurement unit. īecause 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. Modern tests, however, have subsequently improved in reliability. Yet parents of those children thought that the children were still as bright as ever, or even brighter. Some children dropped by 15 IQ points and or by 25 points or more. 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. There were 643 children in the main study group. Children with an IQ above 140 by that test were included in the study. Terman recruited school pupils based on referrals from teachers, and gave them his Stanford–Binet IQ test. įor 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. About 42% of children change their score by 5 or more points when re-tested. Thus, these instruments tend to provide scores that reliably and validly measure the constructs they intend to measure." 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. IQ test publishers use large and "representative samples, use items that measure their intended constructs well, and produce unbiased scores. Both the WAIS-IV and the Stanford-Binet Intelligence Scale, for example, have a reliability of 0.97-0.98 for IQ across all age groups. IQ tests generally are reliable enough that most people 10 years of age and older have similar IQ scores throughout life. (IQ score table data and pupil pseudonyms adapted from description of KABC-II norming study cited in Kaufman 2009. IQ scores can differ to some degree for the same person on different IQ tests, so a person does not always belong to the same IQ score range each time the person is tested. Current IQ test publishers take into account reliability and error of estimation in the classification procedure.ĭifferences in individual IQ classification Some early intelligence classifications by IQ testing depended on the definition of "intelligence" used in a particular case. Those other forms of behavioral observation were historically important for validating classifications based primarily on IQ test scores. There is no standard naming or definition scheme employed universally by all test publishers for IQ score classifications.Įven before IQ tests were invented, there were attempts to classify people into intelligence categories by observing their behavior in daily life. Further, a minor divergence in scores can be observed when an individual takes tests provided by different publishers at the same age. Variability in scores can occur when the same individual takes the same test more than once. When IQ testing was first created, Lewis Terman and other early developers of IQ tests noticed that most child IQ scores come out to approximately the same number regardless of testing procedure. 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. This "deviation IQ" method is 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. An IQ score of 115 means performance one standard deviation above the mean, a score of 85 performance, one standard deviation below the mean, and so on. In the current IQ scoring method, an IQ score of 100 means that the test-taker's performance on the test is of average performance in the sample of test-takers of about the same age as was used to norm the test. IQ classification is the practice of categorizing human intelligence, as measured by intelligence quotient (IQ) tests, into categories such as "superior" or "average". Score distribution chart for sample of 905 children tested on 1916 Stanford–Binet Test
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