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 ( i.e.
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, while a score of 85 means 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 Categorisation of people's intelligence based on IQ
