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Psychological measurement

Psychological measurement is the development of procedures to measure people's characteristics like intelligence or personality. The aptitude for a job or the presence of emotional disturbance can be determined applying standardized tests. Also known as psychological assessment or testing, it can be employed for researching or for predicting a future behavior. To be of utility, a test must meet the conditions of being valid and reliable. Its results must also be compared to a reference group.

A test is valid when it measures what it is supposed to measure. In psychology, there are many qualities that would be interesting to measure, yet it is difficult for psychologists to arrive at a definition. Without a clear and precise definition of the property in question, a test free of ambiguity is difficult to design. Intelligence tests are a well-known example of this difficulty: as psychologists do not agree on the definition of intelligence, the controversies on intelligence test scores are permanent.

Reliability is the condition of giving consistent results over time. During a test's design, it is given to the same people with intervals, and the parts of the test that produce inconsistent results are corrected. To be reliable, a test must be free of subjective considerations. Adjustments may be needed to judging criteria to meet this requirement.

To be meaningful, the result of an individual's test must be compared to an adequate reference group. Such group is usually defined by characteristics such as age, grade in school, or occupation. The results of a comparison group are called 'norms.' Very often the raw result of a test for a person is modified so that it gives immediately the relation with the reference group. Those scores are said to be 'standardized.'

Apart from testing, other activities related with psychological measurement are observation and interviewing. Observation is used primarily with children, but it can also be applied to adults, either alone or in groups. For example, interaction among children can be observed at a playground, or the conduct of a mother and his child can be observed through a one-way mirror. Interviews, although very widely used, do not have the properties of reliability and validity unless they are carried out with these goals in mind, which is not usual. They should, therefore, be used only for orienting purposes.

Types of tests

Test categories include: ability, interest, and personality tests. Ability tests can be further subdivided into skill and performance (or achievement) tests. Skill tests try to measure an innate ability of the person: the intelligence test is the classical example. Two well-known intelligence tests are the Stanford-Binet and the WAIS (Wechsler Adult Intelligence Scale). Achievement tests, on the other hand, try to evaluate a learning process. They are applied in educational institutions to control if goals have been reached, or can be applied for occupational purposes such as selecting people for a job.

Interest tests are widely used in vocational counseling, and are usually given at the end of high school. They include the Strong Vocational Interest Blank and the Kuder Preference Records. Personality tests can be of the paper-and-pencil type or projective tests. Tests of the first group are supposed to be more objective, and assess traits by asking many questions of the true-false or multiple-choice types. The Minnesota Multiphasic Personality Inventory (MMPI) is of this kind.

Projective tests, of which the Rorschach test is the most famous, provide ambiguous stimuli that produce the expression of the subject's real personality. The Rorschach test, for example, consists in meaningless inkblots that are to be interpreted by the subject. The structure, rather than the content, of the responses is analyzed by the tester. The Murray's Thematic Apperception Test (TAT) comprises several pictures of which the subject must make stories. The analysis is usually centered on the role played by the main figure.

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