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Introduces the historical debate on whether intelligence is a single general ability or a collection of distinct skills.
If you are a math whiz, are you more likely to be a great writer too, or are these skills completely separate? The answer reveals whether your brain has a single 'power source' or a collection of independent batteries.
In the early 20th century, psychologist Charles Spearman noticed a curious pattern: people who performed well on one cognitive test (like logic) tended to perform well on others (like vocabulary). To explain this, he proposed the General Intelligence Factor, or ****. According to Spearman, is a single underlying mental energy that fuels all intellectual tasks. However, he also recognized that no one is equally good at everything. He introduced Specific Factors (), which represent specialized talents in specific areas. If you are brilliant at math but only average at music, Spearman would say you have high but a very high specifically for numerical reasoning.
Quick Check
According to Spearman, if a student is a 'straight-A student' across all subjects, what factor are they likely high in?
Answer
The general intelligence factor, or .
Imagine you give a student three tests: 1. Solving a Sudoku puzzle. 2. Calculating a tip at a restaurant. 3. Solving an algebra equation.
If the student scores high on all three, factor analysis would suggest these tests are all measuring one 'Numerical Factor.' Spearman would argue that the common thread across all three is actually the factor.
Not everyone agreed with Spearman. Louis Thurstone analyzed test scores and found that intelligence wasn't just one thing. He identified seven Primary Mental Abilities: Word Fluency, Verbal Comprehension, Spatial Visualization, Number Facility, Associative Memory, Reasoning, and Perceptual Speed. Thurstone argued that a person could be a genius in 'Word Fluency' but struggle with 'Spatial Visualization.' To him, there was no single factor—only a profile of independent strengths. This shifted the focus from 'How smart are you?' to 'How are you smart?'
Quick Check
How does Thurstone's view of a 'genius' differ from Spearman's?
Answer
Thurstone believed a person could be a genius in one specific primary ability without being generally 'smart' in others, whereas Spearman believed a genius would likely perform well across most tasks due to high .
Consider two students: 1. Student A: Scores in the 90th percentile for Math, Verbal, and Spatial tests. 2. Student B: Scores in the 95th percentile for Verbal, but the 30th percentile for Math.
Spearman would focus on Student A as having high . Thurstone would find Student B more interesting, arguing that their high 'Verbal Comprehension' is an independent primary ability that doesn't require high 'Number Facility.'
Look at these hypothetical correlation coefficients () between four tests: - Math and Logic: - Math and Vocabulary: - Vocabulary and Reading: - Logic and Reading:
Based on this, a factor analysis would likely reveal two distinct factors (Quantitative and Verbal) rather than one single . This data would support Thurstone's multi-factor theory over Spearman's unitary theory.
Which statistical technique is used to identify clusters of related items on a test?
If Spearman's theory is correct, what should we see in the correlation between a person's score on a logic test and their score on a vocabulary test?
Louis Thurstone believed that a single 'g' factor was the most important measure of human intelligence.
Review Tomorrow
In 24 hours, try to list all seven of Thurstone's Primary Mental Abilities and explain the difference between and to a friend.
Practice Activity
Look up a sample 'Factor Matrix' online. Try to identify which tests 'clump' together based on high correlation numbers.