History of IQ Test

Thousands of years before the IQ test was devised, attempts were made to evaluate and classify human intelligence. Usually, these attempts were made by observing an individual's appearance, behavior, and speaking habits, but of course these attempts did not have an accurate basis. Therefore, attempts to quantify human intelligence with an accurate basis can be said from the early 1900s.

The First IQ test: Binet-Simon Intelligence Scale

French psychologist Alfred Binet (1857~1911)
French psychologist Alfred Binet (1857~1911)

The first modern IQ test in history was developed in 1904 by French psychologist Alfred Binet and his student Théodore Simon. Alfred Binet is often cited today as one of the most influential psychologists in history.

In the early 1900s, the French government passed a law that all French children to attend school

In the early 1900s, the French government passed laws that all French children to attend school. And there was a need for a way to identify children who needed special education.

Therefore, the French Ministry of Education requested Binet to develop a test that identifies children who are likely to struggle in school. They needed a test to see if the child was actually mentally retarded or normal but lazy.

Shortly after starting development, Binet and Simon discovered that problem-solving tests in areas not taught in school, such as attention, memory, and problem-solving skills, were more predictable of academic success, and developed problems based on them.

While developing the test, they found out interesting phenomena in some kids. Some younger children were able to solve difficult problems that only older children could originally answer, and vice versa. And based on this phenomenon, Binet hypothesized that children basically follow the same developmental pattern but at different speeds of development, and presented a scale of intelligence based on the average abilities of children at a certain age.

Example of Binet-Simon Scale
Example of Binet-Simon Scale

And in 1905, the first IQ test, the Binet-Simon Intelligence Scale, was presented at a conference.

However, contrary to its original purpose, the test developed by Binet was not adopted and used in France. Instead, it aroused great interest when American psychologist Henry H. Goddard, who was head of research at the Vineland School of Education, first established for the study of intellectual disability, translated the test into English in 1908 and distributed it throughout the United States.

Stanford-Binet Intelligence Scale

American psychologist Lewis M. Terman (1877~1956)
American psychologist Lewis M. Terman (1877~1956)

The Binet-Simon Scale was published in a third version until Binet's death in 1911.

Later, in 1916 at Stanford University, psychologist Lewis M. Terman published the Stanford-Binet test, an amendment to the Binet test. While Binet's test was only for children, the Stanford-Binet Test, published by Terman, was a test for Americans that could be applied to adults as well as children. And from this point on, the IQ test can be used as a test to judge giftedness, not just intellectual disability.

After the first Stanford-Binet Scale was published, revised editions were published in 1937, 1973, 1986, and most recently, the fifth edition published in 2003.

The Stanford-Binet Scale even covers non-verbal domains and is considered a fair test of cultural and age differences. Therefore, many intelligence tests since then have been developed greatly influenced by the Stanford-Binet Scale.

The first Group Intelligence Test

Example of The Army Beta tests
Example of The Army Beta tests

Stanford-Binet Scale quickly became the standard intelligence test used in the United States, and was used extensively, especially during World War I.

In World War I, the Army needed a quick way to determine the intellectual abilities of recruits and assign them to appropriate duties. Thus, Terman, Goddard and Robert M. Yerkes together developed the text-based The Army alpha tests and the picture-based The Army Beta tests. The Army tests were used to select officer trainees.

Although the test's fairness and results were poor, the test was conducted on 1.75 million men, making it the first Group Intelligence Tests to be conducted on a large population.

The emergence of the concept of IQ scores

German psychologist William Stern (1871~1938)
German psychologist William Stern (1871~1938)

In 1912, German psychologist William Stern created an intelligence quotient (IQ) to more easily express the results of the Binet-Simon test. The initial IQ score was the mental age score divided by the biological age and expressed as a decimal number. In other words, it was a ratio that compares the degree of individual mental development. Later, to simplify this even further, Terman multiplied the ratio by 100 and added it to Stanford-Binet.

And for today, the IQ score is expressed as the raw score which is transformed to a normal distribution with mean 100 and standard deviation 15.

Disagreement between Binet and Terman

The tests developed by Terman are not designed with good intentions from today's point of view.

Binet thought that human intelligence is not fixed and can be changed sufficiently by education or the surrounding environment. And he developed an intelligence test with the purpose of identifying children with developmental disabilities and providing them with special education to accept them as members of society.

On the other hand, Terman was impressed with Binet's IQ test and his theory, but he thought that intelligence was fixed from birth and could never change. So he developed and distributed tests with eugenics-based intentions to make a better America by identifying people with intellectual disabilities and making them infertile.