Interest in intelligence dates back thousands of years. But it wasn’t until psychologist Alfred Binet was commissioned to identify students who needed educational assistance that the first intelligent quotient (IQ) test was born. Although it has its limitations, and it has many lookalikes that use far less rigorous measurements, Binet’s IQ test is well-known around the world as a way to compare intelligence.
During the early 1900s, the French government asked Binet to help decide which students were most likely to experience difficulty in school. The government had passed laws requiring that all French children attend school, so it was important to find a way to identify children who would need specialized assistance.
Binet and his colleague, Theodore Simon, began developing questions that focused on areas not explicitly taught in schools, such as attention, memory, and problem-solving skills. Using these questions, Binet determined which ones served as the best predictors of school success.
He quickly realized that some children were able to answer more advanced questions that older children were generally able to answer, and vice versa. Based on this observation, Binet suggested the concept of mental age, or a measure of intelligence based on the average abilities of children of a certain age group.
First IQ Test
This first intelligence test, referred to today as the Binet-Simon Scale, became the basis for the intelligence tests still in use today. However, Binet himself did not believe that his psychometric instruments could be used to measure a single, permanent, and inborn level of intelligence.
Binet stressed the limitations of the test, suggesting that intelligence is far too broad a concept to quantify with a single number. Instead, he insisted that intelligence is influenced by many factors, that it changes over time, and that it can only be compared in children with similar backgrounds.
Stanford-Binet Intelligence Test
When the Binet-Simon Scale was brought to the United States, it generated considerable interest. Stanford University psychologist Lewis Terman took Binet’s original test and standardized it using a sample of American participants. This adapted test, first published in 1916, was called the Stanford-Binet Intelligence Scale and soon became the standard intelligence test used in the U.S.
The Stanford-Binet intelligence test used a single number, known as the intelligence quotient (or IQ), to represent an individual’s score on the test. The Stanford-Binet remains a popular assessment tool today, despite going through a number of revisions over the years since its inception.
The IQ score was calculated by dividing the test taker’s mental age by his or her chronological age and then multiplying this number by 100.
For example, a child with a mental age of 12 and a chronological age of 10 would have an IQ of 120 (12/10 x 100).
Pros and Cons of IQ Testing
At the outset of World War I, U.S. Army officials were faced with the task of screening an enormous number of recruits. In 1917, as chair of the Committee on the Psychological Examination of Recruits, psychologist Robert Yerkes developed two tests, known as the Army Alpha and Beta tests.
The Army Alpha was designed as a written test, while the Army Beta was made up of pictures for recruits who were unable to read or didn’t speak English. The tests were administered to over 2 million soldiers1 in an effort to help the Army determine which men were suited to specific positions and leadership roles.
After the war, the tests remained in use in a wide variety of situations outside of the military. For example, IQ tests were used to screen new immigrants as they entered the United States. The results of these tests were unfortunately used to make sweeping and inaccurate generalizations about entire populations, which led some intelligence “experts” to exhort Congress to enact immigration restrictions.
Wechsler Intelligence Scales
Building on the Stanford-Binet test, American psychologist David Wechsler created a new measurement instrument. Much like Binet, Wechsler believed that intelligence involved different mental abilities. Dissatisfied with the limitations of the Stanford-Binet, he published his new intelligence test, known as the Wechsler Adult Intelligence Scale (WAIS), in 1955.
Wechsler also developed two different tests specifically for use with children: the Wechsler Intelligence Scale for Children (WISC) and the Wechsler Preschool and Primary Scale of Intelligence (WPPSI). The adult version of the test has been revised since its original publication and is now known as the WAIS-IV.
The WAIS-IV contains 10 subtests, along with five supplemental tests. The test provides scores in four major areas of intelligence: a verbal comprehension scale, a perceptual reasoning Scale, a working memory scale, and a processing speed scale.
The test also provides two broad scores that can be used as a summary of overall intelligence. The Full-Scale IQ score combines performance on all four index scores, and the General Ability Index is based on six subtest scores.
Subtest scores on the WAIS-IV can be useful in identifying learning disabilities, such as cases where a low score in some areas combined with a high score in other areas may indicate that the individual has a specific learning difficulty.
Rather than scoring the test based on chronological age and mental age, the WAIS is scored by comparing the test taker’s score to the scores of others in the same age group. The average score is fixed at 100, with two-thirds of scores lying in the normal range between 85 and 115.2 This scoring method has become the standard technique in intelligence testing and is also used in the modern revision of the Stanford-Binet test.
Antonson AE. Stanford-Binet Intelligence Scale. In: Clauss-Ehlers CS, ed. Encyclopedia of Cross-Cultural School Psychology. Springer, 2010.
Coalson DL, Raiford SE, Saklofske DH, Weiss LG. WAIS-IV: Advances in the assessment of intelligence. In: WAIS-IV Clinical Use and Interpretation. Elsevier, Inc.; 2010: 3-23. doi:10.1016/B978-0-12-375035-8.10001-1
Fancher RE, Rutherford A. Pioneers of Psychology (5th ed.). W.W. Norton, 2016.