Intelligence Tests. In contrast to tests of specific proficiencies or aptitudes, intelligence tests measure the global capacity of an individual to cope with the environment. Test scores are generally known as intelligence quotients, or IQs, although the various tests are constructed quite differently. The Stanford-Binet is heavily weighted with items involving verbal abilities; the Wechsler scales consist of two separate verbal and performance subscales, each with its own IQ. There are also specialized infantintelligence tests, tests that do not require the use of language, and tests that are designed for group administration.
The early intelligence scales yielded a mental-age score, expressing the child's ability to do as well as average children who were older, younger, or equivalent in chronological age. The deviation IQ used today expresses the individual's position in comparison to a representative group of people of the same age. The average IQ is set at 100; about half of those who take the test achieve scores between 90 and 110. IQ scores may vary according to testing conditions, and, thus, it is advisable to understand results of the tests as falling within a certain range, such as average or superior.
Interest Inventories. Self-report questionnaires on which the subject indicates personal preferences among activities are called interest inventories. Because interests may predict satisfaction with some area of employment or education, these inventories are used primarily in guidance counseling. They are not intended to predict success, but only to offer a framework for narrowing career possibilities. For example, one frequently used interest inventory, the Kudor Preference Record, includes ten clusters of occupational interests: outdoors, mechanical, computational, scientific, persuasive, artistic, literary, musical, social service, and clerical. For each item, the subject indicates which of three activities is best or least liked. The total score indicates the occupational clusters that include preferred activities.
Objective Personality Tests. These tests measure social and emotional adjustment and are used to identify the need for psychological counseling. Items that briefly describe feelings, attitudes, and behaviors are grouped into subscales, each representing a separate personality or style, such as social extroversion or depression. Taken together, the subscales provide a profile of the personality as a whole. One of the most popular psychological tests is the Minnesota Multiphasic Personality Inventory (MMPI), constructed to aid in diagnosing psychiatric patients. Research has shown that the MMPI may also be used to describe differences among normal personality types.
Projective Techniques. Some personality tests are based on the phenomenon of projection, a mental process described by Sigmund Freud as the tendency to attribute to others personal feelings or characteristics that are too painful to acknowledge. Because projective techniques are relatively unstructured and offer minimal cues to aid in defining responses, they tend to elicit concerns that are highly personal and significant. The best-known projective tests are the Rorschach test, popularly known as the inkblot test, and the Thematic Apperception Test; others include word-association techniques, sentence-completion tests, and various drawing procedures. The psychologist's past experience provides the framework for evaluating individual responses. Although the subjective nature of interpretation makes these tests particularly vulnerable to criticism, in clinical settings they are part of the standard battery of psychological tests.
Interpretation of Results
The most important aspect of psychological testing involves the interpretation of test results.
Scoring. The raw score is the simple numerical count of responses, such as the number of correct answers on an intelligence test. The usefulness of the raw score is limited, however, because it does not convey how well someone does in comparison with others taking the same test. Percentile scores, standard scores, and norms are all devices for making this comparison.
Percentile scoring expresses the rank order of the scores in percentages. The percentile level of a person's score indicates the proportion of the group that scored above and below that individual. When a score falls at the 50th percentile, for example, half of the group scored higher and half scored lower; a score at the 80th percentile indicates that 20 percent scored higher and 80 percent scored lower than the person being evaluated.
Standard scores are derived from a comparison of the individual raw score with the mean and standard deviation of the group scores. The mean, or arithmetic average, is determined by adding the scores and dividing by the total number of scores obtained. The standard deviation measures the variation of the scores around the mean. Standard scores are obtained by subtracting the mean from the raw score and then dividing by the standard deviation.
Tables of norms are included in test manuals to indicate the expected range of raw scores. Normative data are derived from studies in which the test has been administered to a large, representative group of people. The test manual should include a description of the sample of people used to establish norms, including age, sex, geographical location, and occupation. Norms based on a group of people whose major characteristics are markedly dissimilar from those of the person being tested do not provide a fair standard of comparison.
Validity. Interpretation of test scores ultimately involves predictions about a subject's behavior in a specified situation. If a test is an accurate predictor, it is said to have good validity. Before validity can be demonstrated, a test must first yield consistent, reliable measurements. In addition to reliability, psychologists recognize three main types of validity.
A test has content validity if the sample of items in the test is representative of all the relevant items that might have been used. Words included in a spelling test, for example, should cover a wide range of difficulty.
Criterion-related validity refers to a test's accuracy in specifying a future or concurrent outcome. For example, an art-aptitude test has predictive validity