History of intelligence testing

The first intelligence tests were created already in the 19th century, but they measured general knowledge rather than intelligence as it is understood today. French psychologist Alfred Binet is regarded as the author of the first professional IQ test. In 1905, doctor Theodor Simon and he created a set of tests aiming to research children’s intellectual development. The tasks were tailored to different age groups. Binet and Simon introduced the notion of a mental age. A ten-year-old child who managed to correctly solve tasks dedicated to a year older age group was in fact eleven in terms of his or her mental age.

A few years later, a German scientist, William Stern, slightly improved the Binet’s IQ tests and introduced a new term to the world of science – intelligence quotient (IQ in short). In order to calculate it, one should use the following formula: divide a person’s mental age by his or her age and multiply the result by 100 in order to avoid troublesome fractions. In this way, a ten-year-old child with the intellect of an eleven year old would have the IQ of 110, in accordance with the (11/10)*100 formula.

Binet’s intelligence tests were useful when researching children, but did not make it possible to examine adults’ intelligence. It resulted from the fact that the concept of a mental age is useless for adults, as they do not develop mentally as fast as children. This process stops already at the age of 16. An American psychologist, David Wechsler, decided to overcome this obstacle and in 1939 devised his own IQ test based on totally different assumptions. He found out that a distribution of intelligence in the population had features of the normal distribution (known as the Gaussian curve). An average intelligence quotient is the most popular, while the number of people with high or low intelligence changes in an inversely proportional manner to the diversion of their IQ levels from the norm.

In the Wechsler scale, the score of 100 is regarded as an average one. Results below 85 mean low intelligence. People with an over-average intelligence level attain scores between 115 and 130. People with high intelligence reach scores between 131 and 145, while geniuses − above 146. In order to become a member of Mensa, i.e. an organization gathering the most intelligent 2% of the population, one should present an intelligence quotient of at least 130.

UNIT 5