๐ Key takeaways
- In 1904 Charles Spearman found that scores on very different mental tasks were positively correlated.
- He proposed a single general factor, g, underlying all these abilities, plus specific factors for each task.
- Spearman invented factor analysis, a statistical method to extract common factors from many test scores.
- The positive correlations (the โpositive manifoldโ) are robust and widely accepted, though researchers still debate what g really represents.
What did Spearman notice?
In 1904 Charles Spearman found that scores on very different mental tasks were positively correlated. People strong in one area tended to be strong in others.
What is the g factor?
He proposed a single general factor, g, underlying all these abilities, plus specific factors for each task. The idea of a general intelligence was born.
How did he find it?
Spearman invented factor analysis, a statistical method to extract common factors from many test scores. It remains central to intelligence research.
Is g still accepted?
The positive correlations (the โpositive manifoldโ) are robust and widely accepted, though researchers still debate what g really represents.
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Last updated: 2026-06-18 ยท โ Reviewed by the All-Lifes editorial team ยท About ยท Methodology