- In 1904 Charles Spearman proposed that a single general factor, which he called g, underlies performance across all mental tasks.
- The positive manifold is the consistent finding that scores on diverse cognitive tests are almost all positively correlated.
- He pioneered factor analysis, a statistical method that extracts the common variance shared by many test scores.
- The positive manifold itself is one of the most replicated findings in psychology, and g remains a useful summary of shared cognitive variance.
What is the g factor?
In 1904 Charles Spearman proposed that a single general factor, which he called g, underlies performance across all mental tasks. In his two-factor theory, each test reflects this shared g plus a factor specific to that particular task.
What is the positive manifold?
The positive manifold is the consistent finding that scores on diverse cognitive tests are almost all positively correlated. Someone strong in one area tends, on average, to be above average in others — the empirical pattern Spearman built g to explain.
How did Spearman find g?
He pioneered factor analysis, a statistical method that extracts the common variance shared by many test scores. The technique is still central to intelligence research and to the design of modern test batteries.
Is g still accepted today?
The positive manifold itself is one of the most replicated findings in psychology, and g remains a useful summary of shared cognitive variance. Researchers still debate what g actually represents — a single cause, an emergent property, or a statistical abstraction — rather than whether the correlations are real.