Raymond Cattell developed a trait theory of personality based on factor analysis. He argued personality developed in 3 phases from intuitive insights to modern experimental methods. Cattell used factor analysis to identify 16 primary traits from questionnaires, tests, and life records. These 16 traits could be further analyzed into 5 secondary factors known as the Big Five: Extraversion, Agreeableness, Neuroticism, Conscientiousness, and Openness. Cattell's research helped establish the scientific study of traits as fundamental dimensions of individual differences.