History
In the late 1800s, Englishman Sir Francis Galton introduced the concept of IQ in the Hereditary Genius book. In 1904, Alfred Binet was asked by the French government to develop an intelligence test to use on children to determine which ones might have difficulty in school; it included many verbally based tasks.
The way to calculate IQ at that time was based on a person's mental age score:
Mental age /Physical age* 100 = IQ score
However, this scoring method later revealed many shortcomings.
To improve this shortcoming, The test was developed in 1916 by Lewis Madison Terman - an American psychologist, Stanford University (in other source, this test was developed in 1912 by Maud Amanda Merril, an American psychologist, professor at Stanford University).
He named his test the Stanford-Binet.
IQ scores are normally distributed with a mean of 100 and a standard deviation of 15 (or 16, 24).
According to this definition:
- about 2/3 of the norm group has scored between IQ 85 and IQ 115
- about 2% of the norm group has scored over 130
- 2% of the norm group has scored under 70.