Analyse your IQ

IQ tests are standardised after being given to many thousands of people, and an average IQ (100) established. A score above or below this norm is used, according to a bell curve, to establish the subject’s actual IQ rating. Because beyond the age of 18 little or no improvement in a person’s IQ rating is found, the method of calculating the IQ of a child is different from the method used for an adult. When the IQ of a child is being measured, the subject attempts an IQ test which has been standardised with an  average score recorded for each age group. Thus a 10-year-old child who scored the results expected of a child of 12 would have an IQ of 120, calculated as follows:

IQ = Mental age(12) x 100 / Chronological age = 120.

However, adults have to be judged on an IQ test whose average score is 100, and their results are graded above and below this norm according to known scores. A properly validated test would have to be given to some 20,000 people and the results correlated before it would reveal an accurate measurement of a person’s IQ. Like most distributions found in nature, the distribution of IQ takes the form of a fairly regular bell curve. On the Stanford–Binet scale which is widely used in the United States, half the population fall between 90 and 110 IQ, half of them above 100 and half of them below; 25 per cent score above 110; 11 per cent above 120; 3 per cent above 130 and 0.6 per cent above 140. At the other end of the scale the same kind of
proportion occurs.