Intelligence and Intelligence Testing for AP Psychology (page 2)
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Since intelligence is a construct, it can only be defined by the behaviors that indicate intelligence, such as the ability to learn from experience, solve problems, use information to adapt to the environment, and benefit from training. Because intelligence tests are common and have been used so widely, they have influenced the definition of intelligence; sometimes a score is used to define someone's intelligence. Intelligence is sometimes reified. Reification occurs when a construct is treated as though it were a concrete, tangible object. Intelligence test developer David Wechsler said, "Intelligence, operationally defined, is the aggregate or global capacity of the individual to act purposefully, to think rationally, and to deal effectively with his environment."
Francis Galton's Measurement of Psychophysical Performance
Modern ability testing originated with Charles Darwin's cousin, nativist Francis Galton, who measured psychomotor tasks to gauge intelligence, reasoning that people with excellent physical abilities are better adapted for survival, and thus highly intelligent. James McKeen Cattell brought Galton's studies to the United States, measuring strength, reaction time, sensitivity to pain, and weight discrimination, using the term "mental test." Although Galton and Cattell's measurements correlated poorly with reasoning ability, they drew attention to the systematic study of measuring cognitive and behavioral differences among individuals. At about the same time, French psychologist Alfred Binet was hired by the French government to identify children who would not benefit from a traditional school setting and those who would benefit from special education. He thought intelligence could be measured by sampling performance of tasks that involved memory, comprehension, and judgment. He collaborated with Theodore Simon to create the Binet-Simon scale, which he meant to be used only for class placement.
Alfred Binet's Measurement of Judgment
Binet thought that as we age, we become more sophisticated in the ways we know about the world and that, therefore, most 6-year-olds answer questions differently from 8-year-olds. As a result of their responses to test items, children were assigned a mental age or mental level reflecting the age at which typical children give those same responses. Although mental age differentiates between abilities of children, it can be misleading when a 6-year-old and an 8-year-old, for example, have mental ages 2 years below their actual (chronological) ages. The younger child would be proportionally further behind peers than the older child. German psychologist William Stern suggested using the ratio of mental age (MA) to chronological age (CA) to determine the child's level of intelligence.
Mental Age and the Intelligence Quotient
In adapting Binet's test for Americans, Lewis Terman developed the Stanford-Binet Intelligence Scale reporting results as an IQ, intelligence quotient, which is the child's mental age divided by his/her chronological age, multiplied by 100; or MA/CA × 100. A 10-year-old who answers questions typical of most 12-year-olds has an IQ score of 120. Another 10-year-old youngster who answers questions typical of an 8-year-old scores 80. With the development of intelligence tests for adults, the ratio IQ becomes meaningless and has been replaced by the deviation IQ determined as a result of the standardizing process for a particular test. For the fifth edition of the Stanford-Binet Intelligence Scale for Adults, the test has been standardized with a representative sample of test takers up to age 90. Fluid reasoning, visual-spatial processing, working memory, and quantitative reasoning seem to peak in the 30s, whereas knowledge seems to peak in the 50s.
The newest version assesses each of five ability areas, such as knowledge, fluid reasoning, and quantitative reasoning, both nonverbally and verbally. By combining these subtest scores, one IQ score is determined.
The Wechsler Intelligence Scales
David Wechsler developed another set of age-based intelligence tests: the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) for preschool children, the Wechsler Intelligence Scale for Children (WISC) for ages 6 to 16, and the Wechsler Adult Intelligence Scale (WAIS) for older adolescents and adults. The latest edition, the WAIS-III, has a verbal scale including items on comprehension, vocabulary, information, similarities, arithmetic, and digit span; and a performance scale including items dealing with object assembly, block design, picture completion, picture arrangement, and digit symbols. Wechsler based his measures on deviation IQs or how spread out the scores were from the mean of 100 (Figure 15.1). Since intelligence has a bell curve distribution, 68% of the population will have an IQ between 85 and 115. These test takers are considered to be low normal through high normal. Test takers who fall two deviations below the mean have a score of 70, typically considered the borderline for mental retardation, while test takers two standard deviations above the mean have scores of 130, sometimes considered intellectually gifted, and those three standard deviations above the mean have scores of 145, sometimes considered geniuses. The Wechsler tests are judged more helpful for determining the extremes of intelligence at the mentally retarded and the genius level than the Stanford-Binet. They also help indicate possible learning disabilities when a child's performance IQ is very different from his/her verbal score.
Some people prefer the term cognitively disabled rather than mentally retarded. Degrees of mental retardation vary from mild to profound. To be considered mentally retarded, an individual must earn a score at or below 70 on an IQ test, and also show difficulty adapting in everyday life. Typically, mildly retarded individuals (about 85%) score between 50 and 70 on IQ tests, are usually able to care for themselves, can care for a home, achieve a sixth-grade education, hold a job, get married, and become an adequate parent. In schools, they are often mainstreamed, or integrated into regular education classes. Moderately retarded individuals (about 10%) score between 35 and 49 on IQ tests; may achieve a second-grade education; may be given training in skills such as eating, toileting, hygiene, dressing, and grooming so that they can care for themselves; and may be given basic training in home management, consumer, and community mobility skills so that they can hold menial jobs and live successfully in a group home. Severely retarded individuals (about 3–4%), with IQs between 20 and 34, typically develop a very limited vocabulary and learn limited self-care skills. Usually they are unable to care for themselves adequately and do not develop enduring friendships. Profoundly retarded individuals (1–2%), with IQs below 20, require custodial care. Communities have been housing a greater proportion of mentally retarded people than in the past. These people live with their own families or in group homes when possible. This deinstitutionalization is termed normalization.
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