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Summary: What is Personality?

Although Gordon Allport claimed to find 50 definitions of personality in his classic 1930s study, he identified three main approaches. Using simpler terminology than Allport, these three approaches are (1) sweeping, all-inclusive "omnibus" definitions (which Allport found useless), (2) the trait approach, and (3) the systems approach (identifying different levels or systems within human personality).

The type of definition Allport dismissed, the omnibus definition, is the only type that includes all available information about a person. It might actually be the best approach to defining personality in the age of big data and AI.

Traits are durable characteristics of an individual. Types are collections of traits that define a category of human being. Types are basically stereotypes. They reflect the customs and fashions of cultures, so they are likely to appear and disappear as cultures change.

Raymond B. Cattell was known for his multivariate analysis of traits. He located 16 dimensions, 15 personality traits plus general intelligence, which could be measured with his 16-PF test.

Cattell believed the two most important traits were extraversion/introversion and anxiety/non-anxiety. Eysenck came to similar conclusions, labeling the same two dimensions extraversion/introversion and stability/instability.

Research in the 1970s and 1980s identified the most important personality traits, defined as traits best able to discriminate between different individ­uals. The result was a convergence of several independent investigative teams on the same list of four traits, five if intelligence is included. This became known as the Big Five.

Thomas Bouchard did a unique study of identical twins separated at birth and raised in separate households. He found that IQ scores and standardized personality test results of the twins he studied were not very similar.

However, in the realm of personal mannerisms, posture, sense of humor, and a variety of quirks and preferences, identical twins were often remarkably similar. This was true even if (as in Bouchard's unique group) they were raised in different families.

In the 1930s, personality tests such as the Rorschach and the MMPI became widely used. The original MMPI was intended to help diagnose psychiatric disorders. Three validity scales aimed to determine whether test-takers were trying to fool an examiner.

The MMPI became the most widely used psychological test, and over 400 new scales were developed, based on the same list of questions. Because it consists entirely of True/False questions, the MMPI can be administered and scored by computer.

However, the MMPI does not measure what most people call personality. For example, identical twins do not necessarily have similar MMPI scores, although most people rate their personalities as very similar. Perhaps "quirks and preferences" are closer to what we call personality than the results of so-called personality tests.

Multiple personality is not necessarily a psychiatric disorder ("dissociative identity disorder") because it does not always cause distress to people. Multiple personality has a long history, with dozens of cases identified before the disorder was popularized by bestsellers in the mid-20th Century.

Recently two perspectives on multiple personality became dominant, and they are not incompatible. One sees multiple personality as a post-traumatic stress disorder of childhood origin. The other sees it as a socially constructed relationship with a therapist or similar figure, involving suggestion.

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