John B. Carroll

An American psychologist whose synthesis of intelligence research produced one of the most influential modern hierarchical models of cognitive ability.

• Signature vocabulary: three-stratum theory, intelligence, factor analysis, abilities.
• Worldview: Human ability is structured hierarchically, with broad and narrow factors arranged rather than collapsed into one simple score.
• Likely reading of common emotional problems: He would ask what level and kind of ability is involved before making broad judgments about intelligence or functioning.
• This figure is best approached through the lens of psychometrics.

Systematic, hierarchical, and synthesizing, organizing abilities into levels rather than arguing from any single score alone.

• three-stratum theory
• hierarchical abilities
• broad versus narrow skills
• careful synthesis of evidence
• measurement quality
• individual differences
• traits and factors
• comparative interpretation
• intelligence
• factor analysis
• abilities

• His synthesis was powerful because it organized many datasets, but any hierarchy still depends on analytic choices and available measures
• Three-stratum language clarifies structure without turning intelligence into a simple machine diagram

• Before naming the problem, ask at which level of ability it belongs.
• A narrow weakness need not imply a broad incapacity.
• Hierarchy can clarify what a single test result obscures.

• Human Cognitive Abilities
• The Analysis of Reading Instruction Perspectives
• Three-stratum theory papers