Intelligence quotient, or IQ, a score that takes into account an individual’s mental and chronological ages. Historically, the first IQ scores employed the following formula, in which MA stands for mental age and CA for chronological age:
IQ score = (MA/CA)100
Using this formula, we can return to the earlier example of a 20 year old performing at a mental age of 18 and calculate an IQ score of (18/20)*100 = 90. In contrast, the 5 year old performing at a mental age at 3 comes out with a considerable lower IQ score: (3/5)100=60.
Intelligence quotient means a score obtained from an intelligence test by dividing the mental age obtained on the test by the actual or chronological age and multiplying by 100, i.e. IQ=cA/ x 100. An IQ score by itself is meaningless; it does not measure intelligence the way a tape measures height, for instance. It is only a measure of comparison between all the people who have taken that particular test, with the average range of scores being placed arbitrarily around 100.