A value which represents the relative (relative to other people the same age as the subject) intelligence of a person. A person's mental age is determined by an intelligence test, then is divided by his chronological age (read: actual age) and multiplied by 100. The resulting value is his IQ. By taking both mental and chronological ages into account, a person of average intelligence, even a child of any age, will be 100. The first widely used intelligence test was based on the Binet-Simon intelligence scale. See IQ.