Measuring intelligence. We can measure the length of something, its volume or its weight with relative ease, since they are directly observable physical attributes.

But, what happens when we try to get a measure of something subjective, such as intelligence or any aspect of an individual’s personality? It is necessary to elaborate mechanisms and techniques that allow us to observe this attribute and obtain a score from which we can work. In the case of cognitive ability, the IQ or IQ is used.

Intelligence: a complex concept

Intelligence is understood as that capacity or set of capacities through which we are able to adapt ourselves correctly and in the most efficient way to the environment, so that thanks to it we are able to analyze, interpret and judge information correctly, develop strategies, adjust our behavior according to our goals and resources and solve problems, among other capacities.

Although the concept of intelligence itself is difficult to delimit (aspects on what it includes, whether it can be modified or not, its link with aspects such as personality or whether it is a unique ability, several hierarchical ones or different independent abilities, for example), it is one of the most valued skills worldwide .

Due to its usefulness in allowing us to adapt efficiently and the observation that not everyone shows the same level of efficiency in the different tasks we undertake, the need to value intellectual capacity arose. This would make it possible, for example, to adjust teaching and learning to the students’ abilities (in fact, this was what caused Binet to be asked to develop the first test to measure intelligence).

The IQ

The Intellectual Quotient or IQ, is, in itself, a measure of intelligence . It is the product of dividing mental age by chronological age and multiplying it by one hundred. In other words, it calculates the approximate age at which most subjects are capable of solving a given problem and it is related to the subject’s real age. Multiplying by one hundred is intended to eliminate decimals.

The result obtained from this operation is called IQ. But the number itself is significant compared to the results obtained by the average of the population of origin. Thus, when we talk about IQ we are actually making a comparison between one’s own performance and that of most individuals of the same age.

The IQ is measured through very diverse and different tests depending on the characteristics of the subjects, the objective of the measurement, their age or if it is intended to evaluate a specific aspect or intelligence at a general level.

One of the best known tests in this respect is the Wechsler scale, the Wechsler Adult Intelligence Scale or WAIS in the case of adult subjects and the Wechsler Intelligence Scale for Children or WISC in the case of children. Total IQ, verbal IQ and manipulative IQ can be measured separately (the former referring to memory and comprehension while the latter is linked to more perceptual and organisational aspects), as well as different indices such as processing speed, verbal comprehension, perceptual reasoning and working memory.

The normal distribution of intelligence from the IQ

The scores obtained in different intelligence tests have to be standardized and moved to a type of distribution that allows us to observe in what relationship the abilities themselves are adjusted to the population average. In the case of the IQ, the normal distribution is used.

It is considered that a value of 100 or approximate values to this would be in the mean , with more than half of the population of the same age having similar scores. Above this measure we would speak of a higher than average capacity, and below it we would be faced with a lower intellectual capacity.

But you have to bear in mind that we are talking about a sock. There is a range within which the scores of people with an equivalent level of cognitive ability can fluctuate. That is why we apply the standard deviation to the normal distribution, which can be understood as the range of dispersion of the scores within the same range. Scores that are at that distance from the mean or will remain within the same range.

The different ranges of intelligence according to IQ

In the case of intelligence, the average would be at 100 and we have a standard deviation of 15. This indicates that people with an IQ between 85 and 115 would still have an intellectual capacity within the average.

People who deviate more than two standard deviations (i.e. with an IQ below 70 or above 130) from the average have capabilities that are significantly different from those of the majority of the population.

Intellectual disability

Subjects with an IQ below 70 are considered to have an intellectual disability . Depending on the expressed IQ, said disability will be of greater or lesser severity. If it is between 70 and 50, the degree of disability is considered to be slight (this being the range in which the majority of the population with intellectual disabilities is found). If we find ourselves with an IQ between 50 and 35, the disability would be moderate, which would imply the need for supervision and special education.

Between 35 and 20 would indicate the existence of a serious intellectual disability, depending on supervision and considering them legally incapacitated. An IQ below 20 is considered to be a profound intellectual disability, which usually occurs with neurological impairments that greatly limit performance and interaction with the environment.

Intellectual giftedness

With regard to subjects above the average, those who manifest an IQ above 130 are considered gifted (although this requires the presence of other attributes such as creativity and the fact that the subject excels in all or most areas, in addition to an IQ above this level).

Subjects with an IQ between one and two standard deviations below the mean are considered borderline intelligence, while those who are somewhere between one and two standard deviations have higher intelligence.

Criticisms of the idea of IQ

The use of IQ as a measure of intelligence has been controversial and disputed since its inception . This is due in the first place because the concept of IQ is based on the conception of intelligence as a general ability.

This means that, although today we tend to think that there is more than one type of intelligence, the final result for the in general we measure the attribute of intelligence follows unitary result and refers to the G (or general) factor. Another controversial aspect is that the tests carried out to measure it, as a general rule, focus on certain abilities that leave aside others such as musical intelligence.

A third aspect to take into account is that there may be cultural biases in the measuring instruments used, despite the fact that they generally try to be as objective as possible. The skills needed to adapt to the environment will vary according to the characteristics of the environment.

Similarly, not everyone has the same concept of intelligence . Thus, an indigenous person living in an Amazon tribe may get very low results simply because the tasks he is asked to perform do not fit his usual reality, even though he can perform better than most people in the forest.

Something similar occurs with illiterate people, or those who have been deprived of stimuli. They are compared to people of the same age, but who have been able to access resources such as formal education. However, the different tests used to measure intelligence try to reduce these biases as much as possible.