History of Intelligence Testing

The first attempts to measure intelligence have been taken in the late nineteenth century. However, the tests from that period are uncertain, because the only check the level of general knowledge not intelligence in the modern sense of the word. Only at the beginning of the twentieth century, French psychologist Alfred Binet developed a set of tasks designed to check the level of mental development of children.

Together with physician Theodore Simon introduced the concept of world of science so-called "mental age". It meant the actual level of intellectual development of the child, corresponding to the average result for a given age group. Mental age didn't have to be the same like chronological age, for example because a child of seven years can be on an intellectual level nine years old.

Several years later, a prominent German psychologist William Stern invented the concept of intelligence quotient. This was the quotient of mental age to the chronological age multiplied by 100. So the mental capacity of seven year old child with the corresponding to the average nine year old child would result 9/7 * 100 = above 128 IQ.

Alfred Binet

The concept proposed by Binet and Stern didn't allow the measurement of adult intelligence. Binet IQ tests were in fact only intended for children, because adults don't grow up intelectually as fast as children. American David Wechsler noted this phenomenon, so he decided to develop its own test. While laying the task took a completely different assumptions. He noted that, distribution of the level of the intelligence in the population corresponds to the characteristics of Gaussian distribution.

People of average intelligence in society is the most and any deviation from the norm are the rarer the more deviate from the average result. Wechsler adopted the average score for the 100 IQ, results above 115 can be considered above average, and above 130 per high. To become a member of Mensa, to be achieved on IQ tests at least 130 points, which goes to only one person on the fifty.