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The Big Five model of personality began with the lexical hypothesis: if a trait matters to human life, language will have a word for it. Sir Francis Galton proposed using language to map traits in the 1880s. In 1933 Franziska Baumgarten pulled more than a thousand terms from German dictionaries, and in 1936 Gordon Allport and Henry Odbert combed Webster’s New International Dictionary page by page for 4,504 trait adjectives. Raymond Cattell cut the list to about 160 terms in the 1940s, and factor analysis, which groups words that tend to appear together, reduced the data to five dimensions in Ernest Tupes and Raymond Christal’s 1950s work with U.S. Air Force officers. Studies in Dutch, German and Finnish found the same five clusters.

The episode walks through openness, conscientiousness, extraversion, agreeableness and neuroticism, and notes that neither end of each scale is simply better. It explains forced-choice questions that are hard to fake, Colin DeYoung’s split of each trait into two aspects, and Cambridge Analytica’s use of the Big Five to target voters in the 2016 U.S. election. Personality also shifts with age: adults tend to become more agreeable and conscientious and less neurotic, extraverted and open, and relationships, divorce or trauma can move these traits.

• Very high openness is linked in studies to greater susceptibility to conspiracy theories and magical thinking.
• Low agreeableness is linked to transactional leadership and high agreeableness to transformational leadership.
• High conscientiousness is the strongest personality predictor of longevity.
• A meta-analysis of more than 75,000 participants tied high neuroticism to depression, anxiety, PTSD and substance abuse.
• A 2023 study found dementia patients with low neuroticism and higher openness, conscientiousness and agreeableness reported better quality of life.