Charles Spearman

Charles Spearman (1863–1945) was an English psychologist who proposed that performance across cognitive tests reflects a general intelligence factor, g, and developed a rank-correlation coefficient.

General intelligence factor: A proposed general mental ability that contributes to performance across different cognitive tasks. Spearman named this shared influence g after studying correlations among test scores.
Intelligence quotient: A standardized score expressing performance on an intelligence test relative to a comparison group. The g hypothesis helped frame debates about what intelligence tests measure.
Multiple intelligences: Howard Gardner’s theory that human intelligence comprises distinct capacities rather than one general ability. Gardner’s framework rejects the emphasis on a single general factor associated with Spearman.
Francis Galton: An English polymath who pioneered statistical approaches to individual differences and heredity. Galton’s measurement of individual differences helped establish questions Spearman pursued with intelligence tests.
Two-factor theory of intelligence: Spearman’s model in which each cognitive performance reflects general ability and a task-specific ability. This theory formalized how Spearman interpreted the positive correlations between mental tests.
Psychometrics: The science of measuring psychological traits, abilities, and behaviors. Spearman’s statistical approach became part of the foundations of psychological measurement.
Primary mental abilities: Louis Thurstone’s model of intelligence comprising several relatively distinct mental abilities. Thurstone challenged the idea that cognitive test performance is chiefly explained by one g factor.
Karl Pearson: An English statistician who developed major methods in correlation and mathematical statistics. Pearson’s statistical work formed part of the mathematical context for Spearman’s correlation methods.
Positive manifold: The empirical tendency for scores on diverse cognitive tests to correlate positively with one another. The pattern Spearman sought to explain became central evidence for his general factor.
Intelligence testing: The use of standardized tasks to assess cognitive abilities and related performance. His work offered a theory for interpreting correlations among test results.

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