The Radex Model of Intelligence

Throughout history, intelligence has been defined in different ways. Today we're going to explore one such method: the Radex model.
The Radex Model of Intelligence
Gorka Jiménez Pajares

Written and verified by the psychologist Gorka Jiménez Pajares.

Last update: 11 June, 2023

Intelligence is a well-studied construct. In fact, psychology professionals have spent years building theories and systems, such as the Radex model, to define intelligence and evaluate it. Indeed, with the birth of psychology in the 19th century, the concept of intelligence became a target of research.

There are three specialized areas of psychology that investigate intelligence. Firstly there’s differential psychology. It investigates elements that, although common to us all, make us different (such as personality). Secondly, there’s developmental psychology. It studies individuals throughout the life cycle. Thirdly, there’s cognitive psychology. It studies mental processes, more especially executive functions.

“The true sign of intelligence is not knowledge, but imagination.”

-Albert Einstein-

man thinking
Sociologist Louis Guttman is the author of the Radex model.


Intelligence is generally defined in two ways. On the one hand, it constitutes a human being’s ability. On the other, it takes the form of behavior in response to the context. In fact, the definition of intelligence differs depending on the researcher studying it. Here are some of the most renowned definitions.

  • Burt claimed it’s a general-type ability. It’s structured in a hierarchy, from the higher and more general levels (such as the g factor ) to the more purely sensitive levels, such as perception (basic sensory and motor skills).
  • Gardner proposes that there are eight kinds of intelligence. As a matter of fact, they could be considered talents. They’re verbal-linguistic, logical-mathematical, visual-spatial, musical-rhythmic, bodily-kinesthetic, interpersonal, intrapersonal, and naturalistic.
  • Sternberg speaks of a practical type of intelligence. It alludes to our ability to adapt to changing environments in order to survive. Intelligence is seen as equivalent to adaptive behavior. This depends on both the person and the context.
  • Eysenck believed that intelligence is biological. This theory suggests that our brains process and transmit the maximum amount of information, with the minimum possible error. In fact, Eysenck considered intelligence to be a matter of neural efficiency.

Scientific research on intelligence suggests that although, throughout life, the percentages vary, we inherit about 40/70 percent of our parents’ intelligence.

However, what about the remaining percentage? Experts claim that 30/60 percent of intelligence that’s unexplained by heredity is based on the environment, our vital experiences, and the challenges that life brings us. Now that we understand the various definitions of intelligence, we’re going to explore the Radex model.

The Radex model: innovation in intelligence

The Radex model was created by Louis Guttman. He was a sociologist and professor of psychological assessment who taught at the University of Jerusalem. He defined intelligence as behavior. More specifically, a behavior that can be observed in different fields and domains according to the capacities that it requires.

The Radex model arose in the 1960s, thanks to innovation in the statistical techniques of factor analysis. Guttman claimed that intelligence can be represented in the form of circles or concentric rings

This model establishes a hierarchy in the form of concentric circles. There are three main domains: spatial-visual skills, verbal ability, and quantitative-numerical ability. The center of the circle represents the g factor of intelligence and the highest point.

The simplex circle

Intelligence is described based on how it’s measured. If we want to measure our ability to solve a puzzle, complete a series of letters, or solve arithmetic calculations, our level of intelligence will depend on how quickly and how well we do it.

In the simplex circle, the tests are organized according to the degree of complexity involved. Among the different tasks that the simplex circle tests evaluate are arithmetic problems (numerical intelligence), constructions via cubes (visual-spatial intelligence), and vocabulary tasks (verbal intelligence).

The circumplex circle

This circle represents the next ring. The tests that it includes are organized according to how similar their contents are. Here, we can find operations with numbers and maze tasks (quantitative intelligence), assembling objects, or completing figures (visual-spatial intelligence), and comprehension and similarity tests (verbal intelligence).

hand holding brain
In the Radex Model, intelligence is represented in the form of concentric circles or rings.

The Radex or intelligent space

Guttman called the combination of simplex and circumplex circles or rings a radex. The Radex Model refers to the ‘radial expansion of complexity’. We can explain it in this way. Every circumference has a radius. Therefore, depending on how close or far the skills required by the tasks are with respect to the center of the circle (the g factor), they’ll be more or less complex.

Thus, an individual is more or less intelligent depending on the position they adopt in the radius of the circumference after carrying out the relevant tests.

“In a Radex space, each test is defined by a position in the circular space according to the complexity and content criteria.”

-Maria del Carmen Carbajo-

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All cited sources were thoroughly reviewed by our team to ensure their quality, reliability, currency, and validity. The bibliography of this article was considered reliable and of academic or scientific accuracy.

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