Theory of General Intelligence or Two - Factor Theory of Intelligence by Charles Spearman - G Factor

Theory of General Intelligence also called the Two Factor Theory.
Spearman observed that students who did well on one mental test usually did well on others too, and those who did poorly on one test tended to do poorly on others also,
Based on this, he came up with the concept of General Intelligence or the common mental ability that affects performance across different tasks.

According to Spearman, the g-Factor represents the core of intellectual ability. It reflects how efficiently a person's brain processes information. People with a high g factor can think abstractly, logically and flexibly. They learn new concepts quickly and solve complex problems easily.

While General Intelligence - g explains similarities in test performance, s factors explain differences in specific skills like maths, vocabulary, spatial visualization, and memory. Spearman believed s factors depend partly on g. So, people with a high g factor are likely to develop specific abilities more easily. However, s factors can also be improved through practice and training, independent of g.

Spearman believed g and s factors work together:
g influences all specific abilities, so students with high g usually do better on tests of specific skills.
s factors rely on g, so students with low g may struggle to develop high specific skills.
However, specific skills can also be improved through focused training, showing that s factors have some independence from g.

Example of Spearman’s Theory
Imagine general intelligence (g) as a car engine. The engine’s power affects how fast the car can go, but the car also needs tires, transmission, and control systems (s factors) to move. This shows that both g (engine power) and s (other parts) impact performance, and neither alone determines how well the car drives—they work together.

In tests, one student may perform well on all subjects, indicating a high g factor. Another student might struggle overall but could improve in a specific area like math with extra practice, even if their g factor remains lower.

Measuring the g Factor
Spearman tested students on various skills like math and memory. He noticed that those who scored well on one test usually did well on others, suggesting a common mental ability (g) influencing all thinking.

He developed a "correlation coefficient" to measure how much test performance relies on g. A score close to 1 or -1 means the test mostly measures g, while a score near 0 means it focuses more on specific skills. He also used "factor analysis" to find the biggest factor (g) that influences performance on multiple tests.

What is IQ
The Stanford-Binet’s Intelligence Quotient Test, which is one of the most popular intelligence tests, aims to measure the g factor. In addition to providing an overall score, the current version of the test also offers a number of score composites as well as subtest scores in ten different areas.
IQ test scores are often interpreted as follows:
40 - 54: Moderately impaired or delayed
55 - 69: Mildly impaired or delayed
70 - 79: Borderline impaired or delayed
80 - 89: Low average intelligence
90 - 109: Average intelligence
110 - 119: High average intelligence
120 - 129: Superior intelligence
130 - 144: Gifted or very advanced intelligence
145 - 160: Exceptionally gifted or highly advanced intelligence
160 and beyond: Genius.

We will learn IQ testing in detail in another video separately,

Impact of General Intelligence,
Researchers believe that general intelligence is linked to overall success in life. Higher intelligence is often associated with better outcomes in Academics, Career, Income and Health.

However, other factors, such as socio-economic status and emotional intelligence, also play a significant role in a person's success, as these factors influence and interact with general intelligence.

Some studies suggest multiple types of intelligence rather than just one g factor.
Alternative models, like Howard Gardner's multiple intelligences or Robert Sternberg's Successful intelligence Model, offer different views.
Critics argue that specific abilities may develop independently of g.
Others say test scores depend more on motivation or luck and not just ability.

Despite the criticisms, the idea of general and specific intelligence in Spearman’s Two Factor theory is still very influential, and IQ testing is widely used as a standard of Intelligence.

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Girish Kishnani
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