IQ is a measure of relative intelligence determined by a standardized test. The first intelligence test was created in 1905 by Alfred Binet and Théophile Simon to determine which French school children were too “slow” to benefit from regular instruction. Binet came up with the idea of mental age when he noticed that children are increasingly able to learn difficult concepts and perform difficult tasks as they get older. Most children reach the same level of complexity at about the same time, but some children are slower reaching those levels. A 6-year-old child who can do no more than a 3-year-old has a mental age of 3. Wilhelm Stern divided the mental age by the chronological age to get a “Mental Quotient.”
Mental Age/Chronological Age = Mental Quotient
A 6-year-old able to do only what a 3-year-old can do has a Mental Quotient of .5 or ½ (3 divided by 6). Lewis Terman later multiplied the Mental Quotient by 100 to remove the fraction and the Intelligence Quotient (IQ) was born!
Mental Age/Chronological Age X 100 = Intelligence Quotient
The 6-year-old with the Mental Quotient of ½ has an IQ of 50.
The majority of people have an IQ between 85 and 115.
