Intelligence Quotient: Characteristics And Evolution

The intelligence quotient (IQ) is a quantitative or statistical representation of an individual’s score on a standardized intelligence test.

The IQ score has been widely used to compare an individual’s intellectual capacity with the average score obtained by a sample of “similar” people, usually of the same age group.

So, for example, it is possible to say that a person’s intelligence, reflected in an IQ test score, is higher (or lower) than the average or typical score of their peers (1).

The fundamentals of the intelligence quotient (IQ)

In 1884, researcher Francis Galton evaluated a large number of people in an attempt to develop an intelligence test. For this evaluation, he tried to measure different characteristics: head size and reaction time are some examples (1).

Through his research, Galton introduced methods for the numerical classification of physical, physiological, and mental attributes. This is how the researcher proposed that a large set of measures of human characteristics could be meaningfully described and summarized using two numbers. 

• First, the mean value of the distribution (the mean).
• Second, the dispersion of scores around this mean value (the standard deviation) (1).

Another of the figures we can place in attempts to measure the intelligence quotient was Charles Spearman. This English psychologist introduced the idea that  all aspects of intelligence are related to each other. This point of view is very important: it laid the groundwork for expressing the intelligence quotient compound (1).

The first intelligence tests and the introduction of the intelligence quotient

The modern era of intelligence testing began just after the turn of the century. Alfred Binet and Theodore Simon were responsible for developing a method to identify substantial differences in the level of intelligence of children.

The idea was to differentiate those who considered intellectually capable of benefiting from education from those who had intellectual problems and should receive special education programs (1).

The methodology involved expressing a child’s performance as a quotient between the score obtained and the age at which the average child could reach the same score. The publication of Binet’s enlarged scale of 1908 and the work of Stern, the German psychologist, gave way to the concept of mental age (MI).

mental age and IQ

A MI of 8 means that the child, regardless of actual age, had the same performance as an 8-year-old on a specific task. This led to the creation of the IQ score to represent a proportion of MI divided by your chronological age (CI). This relationship was put into a metric. Thus, mental age was divided by your chronological age and multiplied by 100, which produced an intelligence quotient or IQ score.

Around 1910, Henry Goddard, principal of a New Jersey school for the mentally retarded, pioneered the concept of IQ testing in the United States. However, the first time IQ scores were part of an intelligence test in the United States was in 1916. On that date, Lewis Terman translated the Binet-Simon test, creating the Stanford-Binet test.

During World War I, the US Army developed the Army’s Alpha and Beta tests. The purpose of these tests was to assign soldiers’ positions based on their intellectual abilities. It also served to discard those deemed intellectually unsuitable for military service.

During that time,  David Wechsler was appointed as a military psychologist. He performed psychological tests on individuals who had failed the army performance scale (3).

Wechsler Tests and IQ Scores

In 1932, Wechsler was appointed chief psychologist at the Bellevue Psychiatric Hospital in New York. From that moment on, a change in the intelligence quotient score began to be considered.

As a result,  the meaning of the IQ score was changed to a standard score. This standard score refers to the mean score obtained by a sample of healthy age pairs  (3). This new conception allows the use of the intelligence quotient throughout life (4).

Today,  these tests are often used to measure intelligence in a way similar to how one would use a meter to measure the length of a table.

However, the question remains: does an IQ score really truly and accurately represent someone’s intelligence? It seems that, little by little, both the intelligence quotient concept and the intelligence quotient are evolving and, with that, the way of evaluating it must also evolve.