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The MMPI or Minnesota Multiphasic Personality Inventory started in the 1930s as the Medical and Psychiatric Inventory published by psychologist Starke R. Hathaway and psychiatrist/neurologist John C. McKinley. It quickly became the most popular personality test among psychologists. However, it is not used as a personality test in the popular sense of giving people insights about their own personality. It was designed specifically to make predictions about treatment outcomes for mental patients. It calls itself a personality inventory because it rates an individual on various traits. The traits are chosen for their utility and importance to mental health treatment professionals.

What is the MMPI? What are advantages of the MMPI?

The main advantage of the MMPI is that it is objective. It consists of 567 true/false statements, so it can be administered by anybody and quickly scored by hand or machine. By contrast, tests like the Rorschach required a skilled examiner, and the scoring was partly subjective, based on the clinical judgment of the person who interpreted the results. The MMPI is easily scored (and in some cases administered) by computer.

Why was the MMPI developed?

Hathaway (quoted in Mednick, Higgins, & Kirschenbaum, 1975, pp. 350-351) said the "real impetus" for developing the test came from reports of insulin shock treatments with schizophrenics. Reports of success of the insulin treatment ranged from zero to 100%. Clearly the hospitals using this treatment did not have any effective way to pick patients who might benefit from the treatment. Hathaway saw a need for an objective diagnostic test that would produce reliable results and allow hospitals to decide who would benefit from particular treatments.

How were items selected for the MMPI?

The true/false items that ended up on the MMPI were initially given to groups of mental patients who had been diagnosed into a well-known psychiatric category (such as depressive or schizophrenic). The responses of these people were compared to responses of normal people such as visitors to the hospital complex and local workers. Only items that discriminated between mental patients and other people were retained in the MMPI.

The ten original, clinical scales of the MMPI measured things like hypochondriasis (the tendency to believe one is ill) and paranoia (suspicion of others). However, the vast amount of data accumulated in the process of refining the MMPI permits the test results to be used for other purposes. Over the years, over 400 new scales have been developed for it. Each scale uses the same MMPI questions but correlates the data with different behavior disorders or personality traits.

How do the validity scales work on the MMPI?

The original MMPI included three validity scales designed to determine whether the test results could be trusted. One scale (the F scale) detects whether the test is being taken seriously or manipulated in an attempt to sound sick. This scale is measured by items that are not frequently endorsed by any psychiatric populations, or which indicate the test is not being taken seriously. One example is, "It would be better if almost all laws were thrown away." Early field-testing showed that nobody who was serious (including psychiatric patients) endorsed such a statement, but people who were answering at random, trying to sound crazy, or joking around often said True to such a statement

Another scale (the L scale, sometimes referred to as the lie scale) asks about things that would be true of most people, such as "I gossip a little at times." A person who answers False to such a statement may be unwilling to reveal anything negative about himself or herself.

Why are the MMPI scales now referred to by number, rather than their original names?

A score of 70 or above on any scale is supposed to indicate a problem which might deserve attention. Today the scales are usually referred to by number, rather than by their original names, because the original names may be misleading. A person who scores high on the schizophrenia scale may not have schizophrenia, as defined by well-known symptoms such as hallucinations and delusional thinking. What one can reasonably say is that a person who scores high on the schizophrenia scale of the MMPI answers true/false questions in a way that resembles past schizophrenic patients. That may or may not turn out to be important, but it is useful information to a clinician.

Other popular personality assessment tools exist. One of the best known is the Myers-Briggs Personality Inventory. It is discussed in connection with Jung's theory of personality traits, later in this chapter.

Personality tests are useful tools, and they have led to thousands of research projects in which test measurements are correlated with other aspects of a person's behavior, such as success of an employee in a business, or likelihood of successfully completing a drug treatment program. However, they do not necessarily measure personality as most people use the term. Recall that Bouchard of Minnesota studied identical twins raised apart from infancy. He found that the single most striking dimension of similarity was personality is defined in an informal and common sense way: their quirks, mannerisms, ways of laughing and holding themselves, temperament. But the twins different in IQ test scores, and they differed on conventional personality tests.

What is a surprising implication from Bouchard's research?

Those conventional personality tests were those we have just described: the Rorschach and MMPI. The implication is clear: those personality tests may have predictive usefulness for a wide variety of purposes, but they do not seem to measure what we naturally call personality. It is an odd thought—personality tests that do not measure personality, as we usually use the term—but that is the implication.

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