- Trait
- A relatively stable, cross-situationally consistent disposition to think, feel, and behave in particular ways. Distinguished from states (temporary, fluctuating conditions) by its endurance across time and situations.
- Lexical hypothesis
- The proposition that the most socially important personality differences are encoded in natural language — that the vocabulary of any culture reflects the traits that matter in that culture. Used by Allport, Cattell, and later researchers to develop data-driven personality taxonomies from personality-descriptive adjectives.
- Allport's trait hierarchy
- Gordon Allport proposed three levels: Cardinal traits (rare, all-pervasive), Central traits (~5–10 characteristic tendencies), and Secondary traits (specific, context-dependent). Allport emphasised the uniqueness of individual personality (idiographic approach).
- Factor analysis
- A statistical technique that identifies clusters of items or variables that correlate with each other, revealing hypothesised underlying dimensions. Used by Cattell (yielding 16 source traits) and later researchers (consistently yielding 5 broad factors) to derive personality taxonomies from large batteries of items.
- Eysenck's PEN model
- A three-factor model proposing Psychoticism (P), Extraversion (E), and Neuroticism (N) as the fundamental dimensions of personality. Each is grounded in biological mechanisms: E in cortical arousal (ARAS), N in limbic reactivity, P in hormonal and serotonergic systems.
- Big Five / OCEAN
- The five-factor model of personality: Openness to Experience, Conscientiousness, Extraversion, Agreeableness, and Neuroticism. Emerged from lexical research and factor analysis across multiple languages. The most widely used personality framework in contemporary research.
- NEO-PI-R
- The NEO Personality Inventory-Revised, developed by Costa and McCrae. The most widely used operationalisation of the Big Five, measuring five domains and 30 specific facets. Self-report and observer-report versions show good convergent validity.
- Conscientiousness
- The Big Five dimension reflecting self-discipline, orderliness, achievement striving, dutifulness, and deliberation. The single best personality predictor of job performance across occupations (Barrick & Mount, 1991) and a robust predictor of health behaviours and longevity.
- Person-situation debate
- The controversy initiated by Mischel (1968), who reviewed evidence that trait-behaviour correlations rarely exceed r ≈ .30. Resolved partly through the interactionist approach: situations moderate trait expression; aggregating behaviour across occasions greatly improves trait prediction.
- Maturity principle
- The finding from longitudinal research (Roberts et al., 2006) that personality changes in socially mature directions across adulthood: Conscientiousness and Agreeableness increase; Neuroticism decreases. Contradicts the view that personality is fixed after age 30.