13.5: Spectrum of Intelligence

The results of studies assessing the measurement of intelligence show that IQ, like many other traits (think height or weight) is distributed in the population in the form of a Normal Distribution (or bell curve), which is the pattern of scores usually observed in a variable that clusters around its average. In a normal distribution, the bulk of the scores fall toward the middle, with many fewer scores falling at the extremes. The normal distribution of intelligence shows that on IQ tests the majority of people cluster around the average (in this case, where IQ = 100), and fewer are either very smart or very dull (see below).

Figure \(\PageIndex{1}\): The majority of people have an IQ score between 85 and 115.[1]

This means that about 2% of people score above an IQ of 130, often considered the threshold for giftedness, and about the same percentage score below an IQ of 70, often being considered the threshold for an intellectual disability.

Intellectual Disabilities

One end of the distribution of intelligence scores is defined by people with very low IQ. Intellectual disability (or intellectual developmental disorder) is assessed based on cognitive capacity (IQ) and adaptive functioning. The severity of the disability is based on adaptive functioning, or how well the person handles everyday life tasks. About 1% of the United States population, most of them males, fulfill the criteria for intellectual developmental disorder, but some children who are given this diagnosis lose the classification as they get older and better learn to function in society. A particular vulnerability of people with low IQ is that they may be taken advantage of by others, and this is an important aspect of the definition of intellectual developmental disorder (Greenspan, Loughlin, & Black, 2001).

One example of an intellectual developmental disorder is Down syndrome, a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. The incidence of Down syndrome is estimated at approximately 1 per 700 births, and the prevalence increases as the mother’s age increases (CDC, 2014a). People with Down syndrome typically exhibit a distinctive pattern of physical features, including a flat nose, upwardly slanted eye, a protruding tongue, and a short neck.

Figure \(\PageIndex{2}\): Down Syndrome is caused by the presence of all or part of an extra 21st chromosome.[2]

Fortunately, societal attitudes toward individuals with intellectual disabilities have changed over the past decades. We no longer use derogatory terms to describe people with intellectual differences, although these were the official psychological terms used to describe degrees of what was referred to as “mental retardation” in the past. Laws such as the Americans with Disabilities Act (ADA) have made it illegal to discriminate on the basis of mental and physical disability.

The normal distribution of IQ scores in the general population shows that most people have about average intelligence, while very few have extremely high or extremely low intelligence.[3]

Giftedness

Being gifted refers to children who have an IQ of 130 or higher (Lally & Valentine-French, 2015). Having an extremely high IQ is clearly less of a problem than having an extremely low IQ but there may also be challenges to being particularly smart. It is often assumed that school children who are labeled as “gifted” may have adjustment problems that make it more difficult for them to create and maintain social relationships.

Figure \(\PageIndex{3}\): Children who get a score on an intelligence test showing an IQ of 130 or higher are labeled as gifted.[4]

As you might expect based on our discussion of intelligence, there are also different types and areas of intelligence and giftedness. Some children are particularly good at math or science, some at automobile repair or carpentry, some at music or art, some at sports or leadership, and so on. There is a lively debate among scholars about whether it is appropriate or beneficial to label some children as “gifted and talented” in school and to provide them with accelerated special classes and other programs that are not available to everyone. Although doing so may help the gifted kids (Colangelo & Assouline, 2009), it also may isolate them from their peers and make such provisions unavailable to those who are not classified as “gifted.”

Testing for high IQ or for disabilities needs to be critically looked at so that the good that these tests were created for are not used for undesirable purposes.[5] Clearly, as mentioned at the start of the discussion on intelligence, much of the research has been tainted in many ways. The APA issued a public apology in Oct 2021 for much of the harms that were initiated and perpetrated by much of the theories, practices and social ills generated and ignored under its auspices. This is an unprecedented move and was clearly long in coming. But the history generated is very telling in how intelligence research and theorists have been particularly egregious contributors to this harm.

There is research that does connect intelligence to academic performance. However there are other factors that have been found to predict academic performance as well - such as motivation (Lavrijsen et al, 2022) and self control (Duckworth & Seligman, 2005). In a separate section we look at different types of testing in schools.

References:

Duckworth, A. L., & Seligman, M. E. P. (2005). Self-Discipline Outdoes IQ in Predicting Academic Performance of Adolescents. Psychological Science, 16(12), 939–944. https://doi.org/10.1111/j.1467-9280.2005.01641.x

Lavrijsen, J., Vansteenkiste, M., Boncquet, M., & Verschueren, K. (2022). Does motivation predict changes in academic achievement beyond intelligence and personality? A multitheoretical perspective. Journal of Educational Psychology, 114(4), 772–790. https://doi.org/10.1037/edu0000666

Attributions:

Child Growth and Development by Jennifer Paris, Antoinette Ricardo, and Dawn Rymond, 2019, is licensed under CC BY 4.0

[1] Image by CNX Psychology is licensed under CC BY 4.0

[2] Image by Vanellus Foto is licensed under CC BY-SA 3.0

[3] Introduction to Psychology - Measures of Intelligence references Psychology by OpenStax CNX, licensed under CC BY 4.0

[4] Image by Ben Mullins on Unsplash

[5] Lifespan Development: A Psychological Perspective by Martha Lally and Suzanne Valentine-French is licensed under CC BY-NC-SA 3.0