What is intelligence?
There is still no standardized scientific definition for the term ‘intelligence’. W. Stern (1911), a pioneer in the field of intelligence, defined intelligence as the ‘general capacity of an individual to consciously adjust his thinking to new requirements’. Intelligence is a hypothetical construct that can only be observed in behavior.
How is intelligence measured?
Intelligence is primarily measured using psychometric tests resulting in a numeric intelligence quotient (IQ tests). They assess a range of cognitive abilities, such as memory, reasoning, problem-solving, and linguistic skills.
To date, the Wechsler Intelligence Scale for Children (WISC) and adults (WAIS), developed by the psychologist David Wechsler, is the most commonly used intelligence test. It is based on the general factor by Spearman and is broadly divided into a verbal subtest and a performance subtest. Accordingly, a verbal IQ and a performance IQ are calculated; their mean makes the full-scale IQ.
Other widely-used tests include:
- Intelligence structure test based on multiple-factor theory by Thurstone
- Culture fair test based on Cattell’s model of crystallized and fluid intelligence
- Progressive matrices test by Raven (1936)
The scores from these tests are usually normalized, meaning the average score in the population is set at 100 with a standard deviation of 15.
It’s important to note that there are many aspects to intelligence and IQ tests are limited in what they actually look at.
The intelligence quotient
Alfred Binet was one of the first persons that attempted to make intelligence measurable. At the beginning of the 20th century, he was commissioned to develop an intelligence test to measure the intellectual capacity of school children. The goal of the test was to identify children with learning disabilities in order to provide them with special individualized help.
The level of difficulty of the test was scaled in ascending order and was supposed to assess the intellectual age of a child with tasks usually passed by 6-year-olds, 7-year-olds, etc.
Based on Binet’s work, William Stern developed the classic intelligence quotient (IQ).
IQ = (mental age / chronological age) × 100
Example: John is 9 years old and solves all the tasks for 11-year-old children → (11/9) × 100 = 122.2
Wechsler’s deviation IQ
David Wechsler later developed the deviation IQ, which is still the most common type of intelligence measurement today. The subject’s score on the intelligence test is compared to the average IQ of people of the same age (the average is standardized to 100 points).
The quotient reflects the subject’s relative position within the selected reference group (e.g., high school students, children in special schools of the same age). Scores obtained from different reference groups are not directly comparable.
What is practical intelligence?
Practical intelligence is the ability to real-world problem-solve and refers less to academic or theoretical knowledge.
Practical intelligence is sometimes referred to as “street smarts.”
Multiple intelligence theory
Howard Gardner’s theory of multiple intelligences proposes that there is not a single definition of intelligence, but that there are several different kinds of intelligences, each important in its own right. This theory has had a significant impact on education, suggesting that teaching methods should vary according to the different intelligences of learners.
What are the 9 types of intelligence?
- Linguistic: using words and language
- Logical-mathematical: thinking logically and solving mathematical problems
- Spatial: visualizing spaces
- Bodily-kinetic: solving problems or creating products with the body
- Musical: performing, composing, and appreciating music
- Interpersonal: understanding and interacting effectively with others
- Intrapersonal: understanding and reflecting self
- Naturalist: recognizing aspects of the natural world
- Existential: capacity to tackle deep questions about existence
Sternberg’s triarchic theory of intelligence
Who developed the triarchic theory of intelligence?
The triarchic theory of intelligence was developed by Robert Sternberg.
Parts of intelligence
The triarchic theory proposes that intelligence is composed of 3 parts:
- Analytical (what is typically measured in IQ tests)
- Creative (dealing with new situations based on experience)
- Practical (adapting to a changing environment)
Spearman’s two-factor theory (1904)
Spearman observed that subjects who were able to easily solve intelligence tasks (calculating) also scored high on other tasks (picture arrangements). From this, he concluded that there must be an inherent cognitive ability.
This intelligence is active in the performance of any task, independent of the type of task. Spearman called this basic ability the general factor of intelligence—the g factor. In hierarchical terms, this g factor is placed above the s factors.
For specific intelligence performances, s factors are necessary. Spearman argued that these s factors do not correlate with each other, meaning that an individual does not necessarily have to perform well or badly in multiple specific areas.
- g factor determines: processing speed, mental capacity, or intellectual performance (‘genius’ or ‘simple character’?)
- s factors determine: spatial, numerical, verbal, and mechanical abilities for specific areas
Thurstone’s multiple-factor theory of intelligence (1938)
Thurstone opposed Spearman’s idea of a superordinate general intelligence factor. Instead, he developed a multiple-factor theory of intelligence that established 7 primary factors. These primary factors are all on the same level.
Thurstone’s 7 primary mental abilities include:
- Number facility
- Verbal comprehension
- Word fluency
- Spatial visualization
- Associative memory
- Reasoning
- Perceptual speed
Jäger’s Berlin model of intelligence structure (1984)
In German-speaking countries, intelligence research was strongly influenced by Jäger’s descriptive model which can be divided into 2 modalities: operational abilities and content-related abilities. Like Spearman, Jäger assumed a superior general factor g. The Berlin Model of Intelligence Structure (BIS) is derived directly from Jäger’s model.
| g factor | |
| 4 Operational abilities | 3 Content-related abilities |
| Memory: active memorization and short-term or medium-term recall or reproduction | Verbal thinking: degree of acquirement and availability of verbal material |
| Creativity: fluid, flexible, inventive production of ideas | Figural thinking: figural, pictographic |
| Processing capacity: ease of processing complex information and concentration | Numerical thinking: degree of acquirement and availability of numerical material |
| Processing speed: speed of operation, speed at which information is processed | |
Cattell’s model of fluid and crystallized intelligence (1971)
Fluid intelligence is the native ability to handle new situations and to solve problems without utilizing previously acquired knowledge. Fluid intelligence is independent of culture and develops during childhood.
Crystallized intelligence describes acquired knowledge. This knowledge is culture-specific with respect to knowledge contents and possible experiences. Crystallized intelligence peaks during adolescence and usually remains constant even in old age.
Note: Crystallized intelligence is retained in old age; fluid intelligence continuously decreases from adolescence onwards.
Bonus: the Dunning–Kruger effect
The Dunning-Kruger effect is a cognitive bias in which people with low ability at a task overestimate their ability. It’s characterized by a lack of self-awareness that prevents someone from accurately assessing their skills. People experiencing this effect are often unable to recognize their own incompetence, leading them to overestimate their own capabilities.
‘If you’re incompetent, you can’t know you’re incompetent … [T]he skills you need to produce a right answer are exactly the skills you need to recognize what a right answer is.’ (David Dunning)
