psychological test, any of a variety of testing procedures for measuring psychological traits and behavior, or for studying some specialized aspect of ability. Several forms of testing have arisen from the need to understand personality and its relationship to psychological disorders.

Projective tests attempt to measure personality based on the theory that individuals tend to project their own unconscious attitudes into ambiguous situations. Best known of the projective tests is that of the Swiss psychiatrist Hermann Rorschach (1884–1922), who used a group of standardized inkblots and asked the client to relate what the pictures brought to mind. The thematic apperception test (TAT), developed by the American psychologist Henry A. Murray, uses a standard series of provocative yet ambiguous pictures about which the client must tell a story. Each story is carefully analyzed to uncover underlying needs, attitudes, and patterns of reaction.

Other personality tests use questionaires that limit the test-taker's responses to "true," "false," or "cannot say." These tests have a much higher level of standardization than projective tests, and hence are often called objective tests. One of the most widely used objective tests is the Minnesota Multiphasic Personality Inventory (MMPI), created in 1942 (and updated in the early 1990s) with the goal of defining a "normal" personality and detecting specific deviances. The test produces profiles that can predict class inclusion for such psychological disorders as schizophrenia, sociopathy, depression, and hysteria. The MMPI has been useful in distinguishing individuals with mental illness from the normal population, but has been less helpful in diagnosing specific disorders.

Behavioral assessments are also used by many psychologists, in which the psychologist observes the individual's actions, usually in a natural setting. Behavior is coded quantitatively—for example, the observer may record the number of times the individual initiates social interactions with others. Such behavior checklists can be used by parents and teachers in evaluating children.

Several diagnostic techonologies are used today to measure brain activity. The electroencephalogram (EEG) records the brain's electrical activity, and its responses to stimuli, through placement of electrodes on the skull. Other brain exams, including the computerized axial tomography (CAT) scan, the positron emission tomography (PET) scan, and the magnetic resonance image (MRI), have shown increasing accuracy in providing detailed pictures of the brain. Such advances may prove indispensable in the understanding of the neurological roots of psychological disorders.

Tests specifically designed to measure abilities include achievement and intelligence tests. Achievement tests measure attainments in a variety of fields, e.g., academic subjects, aptitude for civil service positions. Tests of abilities include intelligence quotient (IQ) tests (see intelligence), spatial-perceptual tests, and motor skills tests. Schools use educational aptitude and achievement tests to compare ability with actual accomplishment, while employers use tests to learn the potential special talents, vocational interests, motor skills, and other such capacities of a prospective employee. Sensory functions, such as visual acuity and hearing, are also measured, and tests have also been devised for special aptitudes, such as memory and creativity.

See L. J. Cronbach, Essentials of Psychological Testing (4th ed. 1984); M. Sokal, Psychological Testing and American Society, 1890–1930 (1987); A. Anastasi, Psychological Testing (6th ed. 1988).