A British scientist, Sir Frances Galton was amongst the first to investigate individual differences in intelligence. He compared them based on awards and achievements. His research convinced him that intelligence was inherited. This further encouraged him to compare the reaction time and range and specificity of the senses, which have since been shown to correlate with academic success.
French scientist, Alfred Binet developed a test to accurately predict academic success when the Government approached him to find out which public school students would have the most problems with formal education. He along with his colleague Theodore Simon, found that the tests of practical knowledge, memory, problem solving, reasoning, and vocabulary, would better test for academic success, rather than the sensory tests done by Galton.
Assuming that all children follow the same stages of development but at different speeds, he and his colleague Simon developed something called the mental age. This meant that if any child answered questions as well as any 12 year old child, he/she had a mental age of 12.
Binet's test was not widely used in France but Henry Goddard the director of a school for mentally challenged children, brought the test to America translated it, and he tested children for mental retardation. Lewis Terman, another American psychologist, adapted the test for use with adults, and developed standards for average ability for each age, which he named the Stanford-Binet Intelligence Scale, for his strong ties with Stanford University.
Instead of giving a person's performance on the Stanford-Binet's Scale as a mental age he converted it to a single number called the intelligence quotient. The idea of the intelligence quotient was given by a german psychologist, William Stern in 1912. A quotient is the result of 1 number divided by another. To find the IQ, the mental age is divided by the actual chronological age and...