The Spearman Theory of Intelligence was a revolutionary psychological theory which revolutionized how we measure intelligence.

Human intelligence has always been of interest to psychologists who seek to understand human understanding.  There have been many theories of intelligence which attempt to measure it in an analytical way.

In the early 1900s, psychologist Charles Spearman developed his theory of general intelligence which identified G, an underlying intelligence factor. G supposedly accounted for the wide range of observable abilities in humans which spoke to humans. G is, therefore, the basis of human intelligence, although there are a number of other factors which contribute to it.

Spearman and the Development of His Theory

In a number of studies, Spearman noticed that children’s grades across their school subject seemed to correlate.  These subjects may be completely different, but there was an overall trend. A child that did well in one subject was more likely to do well in another. In order to find out what that this meant for the nature of intelligence.

He measured the relationships between seemingly different cognitive abilities to test account for the correlations noticed between the scores of individual children. The result was a two-factor theory which sought to show that all cognitive performance can be explained by two variables:

  • G, the general ability
  • S, the specific abilities it gave rise to

Further analysis showed that only g, alone, was needed to explain the correlations between different test scores. G acted as a baseline for an individual’s intelligence, guiding how well a student would achieve in any of their classes.

Uses of the Spearman Theory of Intelligence

Spearman’s theory of intelligence lends itself to two key concepts in psychology.

  1. Psychometrically, g refers to the overall mental capacity for performing tasks.
  2. Statistically, g is a way to account for variance in mental capacity. G has explained up to 50% of the variation of an individual’s performance in IQ tests. This is why, to get a more accurate account of general intelligence, a number of tests must be taken for greater accuracy.

Although intelligence is better understood as a hierarchy, g accounts for the baseline of human intelligence. We may have a greater performance after a good night’s sleep and a healthy meal. However, our overall capacity for performance is governed by G. G, therefore, sits at the bottom of the hierarchy and all other factors are built upon its foundations.

The Evolution of the Theory

G, is now what is referred to when people speak of IQ tests and general mental ability. Spearman’s theory is the foundation of most modern IQ tests, most notably the Stanford-Binet test. These tests include visual-spatial processing, quantitative reasoning, knowledge, fluid reasoning, and working memory.

IQ is generally accepted to be genetic, with high IQ being an inherited trait. However, it is widely known that intelligence is a polygenic trait, with over 500 genes having an influence on the intelligence of any one individual.

Criticism of the Spearman Theory of Intelligence

Spearman’s theory is widely debated due to its postulation of one quantifiable factor which governs human intelligence. In fact, one of Spearman’s own students, Raymond Cattell, was one of his most famed critics.

Cattell felt that general intelligence is in fact split into two further groups, fluid and crystallized. Fluid intelligence was the ability to gain knowledge in the first place, where crystallized knowledge was a sort of knowledge bank of experiences familiar to us. This adaptation of Spearman’s theory has become a more widely accepted theory in intelligence testing and IQ.

Psychologists, Thurstone and Guilford were also critical of Spearman’s general intelligence theory. They believed it was too reductive and that there were several, independent domains of intelligence. However, further examinations into the correlation of test scores suggest a general factor of intelligence.

More modern research has pointed to an underlying mental ability which contributes to cognitive performance. Although not precisely the same as Spearman’s g, the theory of an underlying ability continues to be the prominent theory within psychology.

Other factors which influence intelligence

Aside from general intelligence, which is genetic, there are a number of environmental factors which influence IQ.  Environmental factors such as education, nutrition, and even pollution can have an impact.

It is also possible to increase your IQ score as an adult. A healthy diet and exercise, mentally stimulating games, and meditation have all been shown to increase an IQ score by a few points over the course of a year. On the other hand, things like lack of sleep, alcohol, and smoking have all been shown to decrease IQ within similar timeframes, or even quicker.

Intelligence is not as clear cut as being assigned a number. There are a number of factors which make up your intelligence and a wide range of tests to analyze it.

Spearman’s theory of intelligence changed the way we look at general intelligence. It highlighted that there is some intelligence we are born with and some we develop from our environments. With proper care and some training, it is possible to increase your intelligence and stretch your knowledge.



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This Post Has 2 Comments

  1. Stephen Cooke

    I’m a prime example of someone with a high IQ, which measures general intelligence, but has ended up in a job which doesn’t reflect this IQ level, ie I’m a cleaner, or janitor as they say in the US. I just missed out on entry to Mensa, with an IQ of 144 ( top 3% of the population) on the cartell iii IQ test, So, IQ is not really the best way to ascertain whether a person will be successful, even if they have an high IQ.

  2. Lewis Nickels

    Yeah i did multiple Tests and averaged around an IQ of 146-150 and I still happily work as a childcare worker changing nappies etc.
    This just shows that an IQ has little to do with practical intelligence and is only really theoretical such as in a test.

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