In psychology, personality type refers to the classification of individuals into distinct categories based on qualitative differences, such as introverts and extraverts being fundamentally different. This contrasts sharply with personality trait theories, which view individual differences as quantitative variations along continuous dimensions.
The concept of personality types remains highly controversial among researchers, as most personality test scores tend to fall on a bell curve rather than forming discrete categories. Consequently, personality type theories have largely fallen out of favor, with many researchers finding trait-based instruments, like the Five-Factor Model, to be more effective predictors of clinically relevant information than type-based assessments such as the MBTI.
Historically, prominent type theories include Galen's Four Temperaments and the Type A/Type B personality theory, which initially suggested Type A individuals were more prone to heart disease—a claim later disproven by empirical research. Today, the majority of psychologists favor trait models for their ability to more accurately and comprehensively explain the diversity of human personality.