From Wikipedia, the free encyclopedia. In psychology, trait theory (also called dispositional theory) is an approach to the study of human personality. Trait theorists are primarily interested in the measurement of traits, which can be defined as habitual patterns of behavior, thought, and emotion. Eysenck Personality Questionnaire, (the three-factor model). 2  Using factor analysis Hans Eysenck suggested that personality is reducible to three major traits: neuroticism, extroversion, and psychoticism. 3  Big Five personality traits, (the five-factor model).