Introduction
Although means for measuring mental ability date as far back as 2000 BCE, when the ancient Chinese administered oral tests to determine a candidate’s fitness for carrying out the tasks of civil administration, the modern intelligence test has its origins in the nineteenth century, when Jean-Étienne-Dominique Esquirol drew a clear distinction between mentally deranged people, or “lunatics,” and intellectually disabled people, deemed “idiots.” Esquirol believed that it was necessary to devise a means of gauging “normal” intelligence so that deviations from an agreed-on norm could be ascertained, and he pointed out that intellectual ability exists on a continuum extending from idiocy to genius. His work coincided with studies in Europe and the United States that were designed to develop a concept of intelligence and to fashion a means of testing this capacity. Work done by Sir Francis Galton in the United Kingdom on hereditary genius, by James McKeen Cattell in the United States on individual differences in behavior, and by Hermann Ebbinghaus in Germany on tests of memory, computation, and sentence completion culminated in the 1905 Binet-Simon scale, created by Alfred Binet
and Théodore Simon. It was the first practical index of intelligence measurement as a function of individual differences. This test was based on the idea that simple sensory functions, which had formed the core of earlier tests, are not true indicators of intelligence and that higher mental processes had to be included.
The Binet Tests
French psychologist and educator Binet founded the first French psychological laboratory. He was a pioneer in the study of individual differences in abilities and introduced intelligence tests that were quickly accepted and widely used in Europe and the United States. His work stemmed from a commission from the minister of education in Paris, who gave him the task of devising a way to distinguish between idiocy and lunacy, as Esquirol had defined them, and normal intelligence, so that handicapped students could be given special instruction. Binet and Simon used many items that had been developed by earlier examiners; the key advances they made were to rank items in order of difficulty and to register results in terms of age-based cognitive development. Their scale reflected the idea that intelligence was a combination of faculties—judgment, practical sense, and initiative—and contained measures related to memory, reasoning ability, numerical facility, and object comparison.
Binet and Simon’s work demonstrated the feasibility of mental measurement, assessing intelligence for the first time in general terms rather than measuring its component parts. Binet revised the test in 1908, and another revision was published in 1911, the year of his death. Advances in his basic design led to the development of tests that could be used for all children (not only those considered mentally limited) in assessing their “mental quotient,” a ratio adapted by Lewis Terman of Stanford University. It was obtained by dividing mental age (as determined through scores on a test) by chronological age. Terman renamed it the intelligence quotient (IQ), and his 1916 version of the Binet-Simon scale became known as the Stanford-Binet test, the most common intelligence test administered in the United States. It was revised and updated in 1937, 1960, 1972, and 1986, when a point-scale format was introduced for the first time.
The Wechsler Tests
Binet’s test depended on an age scale; that is, the questions that were answered correctly by a majority of ten-year-old children were assigned to the ten-year age level of intelligence. A more sophisticated version of the test devised by Robert Yerkes depended on a point scale for scoring; this format was fully developed by David Wechsler. While the Binet-Terman method used different tests for different age groups, Wechsler worked toward a test to measure the same aspect of behavior at every age level. The goal of his test was to measure intelligence in a holistic (encompassing the larger whole of personality) fashion that did not depend on the verbal skills that the Stanford-Binet tests required. Wechsler thought of intelligence as a multifaceted complex of skills, the total of an effective intellectual process; he wanted his test to show the way intelligent people behaved as a consequence of an awareness of the results of their actions. He thought that those actions would be more rational, worthwhile (in terms of social values), and meaningful than those of less intelligent people.
Wechsler’s first test (the Wechsler-Bellevue Intelligence Scale) was published in 1939, and it awarded points for each answer depending on the level of sophistication of the response. The test consisted of six verbal subjects (information, comprehension, arithmetic, similarities, vocabulary, and digit span) and five performance subtests (picture completion, picture arrangement, block design, object assemblies, and digit symbols). The division into verbal and performance skills permitted the calculation of three intelligent quotients: a verbal IQ based on the sum of the verbal tests, correlated with norms of age, a performance IQ based on the sum of performance tests, and a full-scale IQ derived from the sum of all the answers. The test was standardized on a sample of adults, and it could be used to test individuals who had linguistic or sensorimotor handicaps. The pattern of scores on the separate tests could also be used to diagnose learning disability or, in some situations, clinical disorder or dysfunction.
The original test was limited by the sample used for standardization, but the 1955 Wechsler Adult Intelligence Scale (WAIS) provided a basis for testing adults from the ages of sixteen to seventy-five. Further revision in the standard scale (including the WAIS-R, 1981) updated the test to coincide with changes in cultural experience. In addition, a Wechsler Intelligence Scale for Children (WISC) was designed to cover ages five to fifteen in 1949 and was revised (WISC-R) in 1974 to cover ages six to sixteen. In 1991, another revision (WISC-III) was introduced. Subsequent modifications also led to a test suitable for preschool children, the Wechsler Preschool and Primary Scales of Intelligence (WPPSI) of 1967, which covered ages four to six and a half and included mazes, animal figures, and geometric designs. This test was revised in 1981 (WPPSI-R) to extend its range over three years to seven years, three months. Further adjustments have also been made to account for a candidate’s sociocultural background in a test called the System of Multicultural Pluralistic Assessment (SOMPA, 1977).
Recent definitions of intelligence have resulted in further development of testing instruments. Raymond Cattell’s proposal that intelligence could be divided into two types—fluid (or forming) and crystallized (fixed)—led to a test that used figure classification, figure analysis, and letter and number series to assess the essential nonverbal, relatively culture-free aspects of fluid intelligence; it used vocabulary definition, abstract word analogies, and general information to determine the skills that depend on exposure to cultural processes inherent in crystallized intelligence. Other theories, such as Jean Piaget’s
idea that intelligence is a form of individual adaptation and accommodation to an environment, led to the development of a test that measures mental organization at successive ages.
Uses of Intelligence Assessment
There was a tendency at various times to regard intelligence assessment as an answer to questions of placement and classification in almost every area of human experience. The most effective and scientifically valid uses of tests, however, have been in predicting performance in scholastic endeavor, in revealing disguised or latent ability to assist in career counseling, in determining the most appropriate developmental programs for handicapped or mentally handicapped individuals, in locating specific strengths and weaknesses in an individual, in measuring specific changes associated with special programs and forms of therapy, and in comparing a child’s mental ability with other children observed in a similar situation to establish a profile of cognitive skills.
One of the most widespread and effective uses of intelligence tests is the determination of possible problems in a child’s course of basic education. As reported by Lewis Aiken in Assessment of Intellectual Functioning (1987), a typical case involved an eight-year-old boy with a suspected learning disability. He was given the WISC-R test in 1985, and his full-scale IQ was figured to be 116, placing him in the high average classification. This provided an assessment of general intelligence and scholastic aptitude. His verbal IQ was 127, placing him in the ninety-seventh percentile, indicative of exceptional verbal comprehension. This suggested that he could reason very well, learn verbal material quickly, and process verbal information effectively. His performance IQ of 98 placed him in the average category, but the magnitude of the difference between his verbal and performance IQs is very unusual in children of his age. It pointed to a need for additional interpretive analysis, as well as further study to reveal the reasons behind the discrepancy. Close scrutiny of the test results showed that low scores on the arithmetic, digit span, and coding subtests might indicate a short attention or memory span, poor concentration, or a lack of facility in handling numbers. While no absolute conclusions could be drawn at this point, the results of the test could be used in conjunction with other procedures, observation, and background information to determine an appropriate course of action.
Intelligence and Guidance
Another common use of an intelligence test is to help an examinee determine specific areas of ability or aptitude that might be useful in selecting a career route. As reported in Aiken, a college senior was given the Otis-Lennon School Ability Test (O-LSAT, Advanced Form R) just before her twenty-second birthday. She planned to enroll in a program in a graduate business school and work toward a master of business arts degree. The O-LSAT is designed to gauge general mental ability, and it includes classification, analogy, and omnibus (a variety of items to measure different aspects of mental functioning) elements. The omnibus includes verbal comprehension, quantitative reasoning, and the ability to follow directions. The examinee was able to complete the test in thirty-five minutes and used the remaining allotted time to check her answers. Her raw score (number of items answered correctly) was 64 (out of 80), her school ability index was 116—which approximated her IQ—and her percentile rank among candidates in the eighteen-plus range was 84. These scores were in the average range for college seniors, indicating an overall intellectual ability that could be classified as “high average” in terms of the general population. Of the sixteen items answered incorrectly, a superficial analysis pointed toward some difficulty with nonverbal reasoning, but no conclusions could be reached without further examination in this area. There was no significant pattern of errors otherwise, and the random distribution offered no additional guide to areas of weakness. The initial conclusion that was drawn from the test was that a career in business was appropriate, and that with hard work and the full application of her intellectual abilities, she would be able to earn an M.B.A. at a reputable university.
A particularly important application of intelligence assessment is the identification and guidance of a child with advanced intellectual abilities. In a case reported in Jerome M. Sattler’s
Assessment of Children (1988), a three-year-old boy was tested repeatedly from that age until his sixth birthday. This procedure required the implementation of the Stanford-Binet Form L-M, the WPPSI, and the Peabody Individual Achievement Test (PIAT) for grade equivalents. The Stanford-Binet scores were 127 (at age three), 152, 152, and 159+ (with a linear extrapolation to 163). During his first test he was anxious and did not give long verbal responses, but the range of his scores indicated a very superior classification. He did not cooperate with the examiner on the WPPSI vocabulary and animal subtests (the examiner believed that he was not interested), but his performance at age four placed him in the superior range. On the PIAT, he was consistently above average, earning a grade equivalent above 4.0 at the age of six, with a grade equivalent of 7.4 (his highest score) in mathematics; the average grade equivalent for age six is 1.0.
As Sattler points out, the case illustrates “a number of important principles related to testing and assessment.” In the largest sense, it illustrates the way different tests measuring general intelligence may yield different results (although all pointed toward superior mental development). The same test may also yield different scores at different age levels. The child’s motivation (among other factors) may also play an important part in his results. More specifically, since the boy showed more interest in reading at age three and mathematics at age six, the test could not be considered a useful predictor of later interest, although an interest in solving perceptual-logical problems remained consistent throughout. Finally, since the parents had kept a detailed record of the boy’s early development in a baby book, the rich history recorded there was corroborated by the test results that reaffirmed their initial suspicions that the boy was unusually gifted. During his first year in school, he tended to play alone and had frequent minor tantrums that affected his performance in school subjects. When he became accustomed to the social process of school life, however, he was able to demonstrate the ability that his parents had observed at home and that the initial tests validated.
Definitions of Intelligence
While intelligence tests of some sort appeared in human history as early as the Old Testament book of Judges (7:3–7, 12:6), which indicates that early Jewish society used questions and observations in personnel selection, the intelligence test as it is known today can be traced to Renaissance Europe. In 1575 the Spanish physician Juan Huarte wrote Examen de Ingenios, a treatise concerning individual differences in mental ability with suggestions for appropriate tests. His work, and that of other investigators and theorists, was the result of the rise of a middle class with aspirations to productive employment. Previously, the aristocracy had controlled everything, and fitness for a position was determined by lineage. Once this monarchical rule began to break down, other means were necessary for determining who was fit for a particular occupation and what might be the most productive use of a person’s abilities. When it became apparent that royal blood was no guarantee of competence, judgment, or mental acuity, the entire question of the origins of intelligence began to occupy members of the scientific community. For a time, the philosophy of empiricism led scientists toward the idea that the mind itself was formed by mental association among sense impressions, and sensorimotor tests were particularly prominent. As the results of these tests failed to correlate with demonstrations of mental ability (such as marks in school), however, other means were sought to measure and define intelligence. The interest in intelligence testing in the nineteenth century was an important aspect of the development of psychology as a separate scientific discipline, and the twin paths of psychometric (that is, the quantitative assessment of an individual’s attributes or traits) and statistical analysis on one hand and philosophical conjecture concerning the shape and operation of the mind on the other were joined in experimentation concerning methods of assessing intelligence.
From their first applications in France as a diagnostic instrument, intelligence tests have been used to help psychologists, educators, and other professionals plan courses of action to aid individuals suffering from some mental limitation or obstacle. This role has been expanded to cover the full range of human intellectual ability and to isolate many individual aspects of intelligence in myriad forms. The profusion of tests has both complicated and deepened an understanding of how the mind functions, and the continuing proposition of theories of intelligence resulted in an increasingly sophisticated battery of tests designed to assess and register each new theory.
Modern Testing
In addition, technological developments, particularly the growing use of computers, permit a wider use of flexible testing in which the decision about what item or task to present next depends on the previous answer. Computers are also useful in “number crunching,” so that such basic components of a test system as norms, derived scores, and reliability and validity coefficients (the basic statistical material behind the calculation of scores) can be assembled more quickly and efficiently. Computers also make it possible to administer tests at multiple sites simultaneously when an individual examiner’s presence is not necessary. Nevertheless, the human capacity for judgment and analysis in the interpretation of results remain crucial to test procedures.
Intelligence testing is likely to continue as a primary means of predicting educational or vocational performance, but tests designed to measure the mind in terms of its ability to process information by shifting strategies in response to a changing environment are likely to become more prevalent. The proliferation of more detailed, separate sets of norms for different groups (age, sex, ethnic origin, and so on) is likely to continue. Also, the relationship between intelligence per se and behavioral attitudes that seem to resemble aptitude rather than personality measures is part of the heredity-environment controversy that will continue. Finally, advances in studies on the neurophysiological bases of intelligence will be reflected in tests responsive to a growing understanding of the biochemical aspects of cognition. As an operating principle, though, professionals in the field will have to be guided by a continuing awareness that intelligence testing is only one aspect of understanding a person’s total behavior and that the limitations involved in the measuring process must be understood to avoid incorrect or inappropriate diagnoses that might prove harmful to an individual.
Howard Gardner postulated a theory of multiple intelligences
that focuses on a symbol system approach combining both factor analytic and information-processing methodology. He included seven dimensions of intelligence: verbal and linguistic, mathematical and logical, visual and spatial, body and kinesthetic, musical and rhythmical, interpersonal and intrapersonal, and environmental. The concept of types of intelligence is not new. L. L. Thurstone developed a test of eight scales named the Primary Mental Abilities test. Edward L. Thorndike identified several types of intelligence: abstract, social, and practical. Sternberg used informational processing and cognitive theory in his model of intelligence and identified three different types of information-processing components: metacomponents, performance components, and knowledge-acquisition components. He saw metacomponents as the higher-order control processes used to oversee the planning, monitoring, and evaluation of task performance.
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