outofservice.com/bigfive
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The Big Five page on Out of Service focuses on the Big Five personality traits (OCEAN). It provides explainers for each trait and related resources, such as psychometric tests and articles on applying the model.
More resources on Personality
Open Psychometrics
An independent site hosting public-domain personality inventories alongside the raw anonymized response data from everyone who took them. Useful for both self-assessment and for practising factor analysis on real psychometric datasets.
The Personality Project
William Revelle's Northwestern University site surveying personality theory, measurement, and research methods, with course notes, reading lists, and R tutorials. It maps how the field's major models and psychometric techniques fit together.
Personality
An undergraduate textbook pairing each major theoretical approach — psychoanalytic, trait, biological, humanistic, behavioral, cognitive — with the research program it produced. Readers finish able to compare the approaches and judge how personality is actually measured.
personality.org
Personality.org is an educational resource on personality psychology that provides clear explanations of theories, trait models, and assessment methods. It features articles and guides for learners seeking to understand how personality is studied and measured.
ipip.ori.org
Public-domain personality assessments drawn from the International Personality Item Pool (IPIP), hosted by Oregon Research Institute. The site offers free Big Five and other personality scales, item banks, scoring instructions, and research resources.