The correlation between IQ scores and vocational success is BEST described as

3.3 The Distribution of IQ Scores

Intelligence test scores follow an approximately normal distribution, meaning that most people score near the middle of the distribution of scores. Scores drop off fairly rapidly in frequency in either direction from the center of the distribution. For example, on the IQ scale, approximately two-thirds of all scores fall between IQs of 85 and 115 and approximately 95% of all scores fall between IQs of 70 and 130. Put another way, only 1 of 20 scores differs from the average IQ (100) by more than 30 points.

It has been common to associate certain levels of IQ with labels. For example, at the upper end, the label “gifted” is sometimes assigned to people with IQs over a certain point such as 130. At the lower end, mental retardation has been classified into various degrees depending on IQ so that, for example, IQs of 70 to 84 have been classified as borderline retarded, IQs of 55 to 69 as mildly retarded, IQs of 40 to 54 as moderately retarded, IQs of 25 to 39 as severely retarded, and IQs below 25 as profoundly retarded.

Many psychologists now believe that IQ represents only a part of intelligence and that intelligence is only one factor in both mental retardation and giftedness. Most current definitions of mental retardation stress adaptive skills as well as IQ, and they also emphasize attributes such as creativity, motivation, and achievement in conceptions of giftedness.

Kaufman Adolescent and Adult Intelligence Test (KAIT)

The KAIT (Kaufman & Kaufman, 1993), is an individually administered intelligence test for individuals between the ages of 11 and more than 85 years. It provides Fluid, Crystallized, and Composite IQs, each a standard score with a mean of 100 and a standard deviation of 15.

Theory. The Hom-Cattell theory forms the foundation of the KAIT and defines the constructs presumed to be measured by the separate IQs; however, other theories guided the test development process, specifically the construction of the subtests. Tasks were developed from the models of Piaget’s formal operations (Inhelder & Piaget, 1958; Piaget, 1972) and Luria’s (1973, 1980) planning ability in an attempt to include high-level decision making on more developmentally advanced tasks. Luria’s notion of planning ability involves decision making, evaluation of hypotheses, and flexibility, and “represents the highest levels of development of the mammalian brain” (Golden, 1981, p.285).

Piaget’s formal operations depicts a hypothetical-deductive abstract reasoning system that has as its featured capabilities the generation and evaluation of hypotheses and the testing of propositions. The prefrontal areas of the brain associated with planning ability mature at about ages 11 to 12 years (Golden, 1981), the same ages that characterize the onset of formal operational thought (Piaget, 1972). The convergence of the Luria and Piaget theories regarding the ability to deal with abstractions is striking; this convergence provided the rationale for having age 11 as the lower bound of the KAIT, and for attempting to measure decision making and abstract thinking with virtually every task on the KAIT (Kaufman & Kaufman, 1993).

Within the KAIT framework (Kaufman & Kaufman, 1993), Crystallized intelligence “measures the acquisition of facts on problem solving ability using stimuli that are dependent on formal schooling, cultural experiences, and verbal conceptual development” (p.7). Fluid intelligence “measures a person’s adaptability and flexibility when faced with new problems, using both verbal and nonverbal stimuli” (Kaufman & Kaufman, 1993, p. 7). It is important to note that this Crystallized-Fluid construct split is not the same as Wechsler’s (1974, 1981, 1991) verbal-nonverbal split. More specifically, the KAIT Fluid subtests stress reasoning rather than visual-spatial ability, include verbal comprehension or expression as key aspects of some tasks, and minimize the role played by visual-motor speed for correct responding.

The Core Battery of the KAIT is composed of three Crystallized and three Fluid subtests, and these six subtests are used to compute the IQs. The Expanded Battery also includes two supplementary subtests and two measures of delayed recall that evaluate the individual’s ability to retain information that was learned previously in the evaluation during two of the Core subtests.

The Core Battery of the KAIT consists of subtests one through six, and subtests one through ten comprise the Expanded Battery. Each subtest except the supplementary Mental Status task yields age-based scaled scores with a mean of ten and a standard deviation of three. Sample and teaching items are included for most subtests to ensure that examinees understand what is expected of them for each subtest.

The delayed-recall subtests are administered, without prior warning, about 25 and 45 minutes after the administration of the original, related subtests. The two-delayed recall subtests provide good measure of an ability that Horn (1985, 1989) calls TSR (Long-Term Storage and Retrieval). TSR “involves the storage of information and the fluency of retrieving it later through association” (Woodcock, 1990, p. 234).

The Mental Status subtest is comprised of ten simple questions that assess attention and orientation to the world. Most normal adolescents and adults pass at least nine of the ten items, but the task has special use with retarded and neurologically impaired populations. The Mental Status subtest may be used as a screener to determine if the KAIT can be validly administered to an individual.

Standardization and Properties of the Scale. The KAIT normative sample, composed of 2,000 adolescents and adults between the ages of 11 and 94 years, was stratified on the variables of gender, racial/ethnic group, geographic region, and socioeconomic status (Kaufman & Kaufman, 1993).

Mean split-half reliability coefficients for the total normative sample were .95 for Crystallized IQ, .95 for Fluid IQ, and .97 for Composite IQ (Kaufman & Kaufman, 1993). Mean test-retest reliability coefficients, based on 153 identified normal individuals in three age groups (11–19 years of age, 20–54 years of age, 55–85 + years of age), retested after a one-month interval, were .94 for Crystallized IQ, .87 for Fluid IQ, and .94 for Composite IQ (Kaufman & Kaufman, 1993). Mean subtest split-half reliabilities of the four Crystallized subtests ranged from .89 to .92 (median = .90). Mean values for the four Fluid subtests ranged from .79 to .93 (median = .88) (Kaufman & Kaufman, 1993). Median test-retest reliabilities for the eight subtests, based on the 153 people indicated previously, ranged form .72 to .95 (median = .78). Rebus Delayed Recall had an average split-half reliability of .91 and Auditory Delayed Recall had an average value of .71; their respective stability coefficients were .80 and .63 (Kaufman & Kaufman, 1993).

Factor analysis, both exploratory and confirmatory, gave strong construct validity support for the Fluid and Crystallized Scales, and for the placement of each subtest on its designated scale. Crystallized IQs correlated .72 with Fluid IQs for the total standardization sample of 2,000 (Kaufman & Kaufman, 1993). Table 4.4 provides the correlations of the three KAIT IQs with standard scores and IQs yielded by other major intelligence tests. The data found in this table are taken from the KAIT Technical Manual (1993). The values shown in Table 4.4 support the construct and criterion-related validity of the three KAIT IQs.

Table 4.4. Correlations of the Three KAIT IQ with Standard Scores and IQs yielded by Other Major Intelligence Tests

INTELLIGENCE TESTAGE RANGECRYSTALLIZEDFLUIDCOMPOSITEWAIS-R Verbal IQ (N = 343)16–830.780.620.76WAIS-R Performance IQ (N = 343)16–830.720.720.77WAIS-R Full Scale IQ (N = 343)16–830.860.730.85WISC-R Verbal IQ (N = 118)11–160.790.740.83WISC-R Performance IQ (N = 118)11–160.670.670.72WISC-R Full Scale IQ (N = 118)11–160.780.750.82K-ABC Mental Processing Composite (N = 124)11–120.570.620.66K-ABC Achievement (N = 124)11–120.810.640.82SB-V Test Composite (N = 79)11–420.810.840.87

Note: Data in this table are based on data reported in the KAIT Manual (Kaufman & Kaufman, 1993, Tables 8.15–8.19 and 8.22–8.23. Data for the WAIS-R are averages of values reported separately for four age groups between (a) 16 and 19 years and (b) 50 and 83 years.

The KAIT benefits from an integration of theories that unite developmental (Piaget), neuropsychological (Luria), and experimental-cognitive (Hom-Cattell) models of intellectual functioning. The theories work well together and do not compete with one another. Together, the theories give the KAIT a solid theoretical foundation that facilitate test interpretation across the broad 11 to 94 year age-range on which the battery was normed.

The KAIT and WISC-R were administered to 118 individuals ages 11 to 16 years, and the KAIT and WAIS-R were administered to 338 individuals ages 16 to 83 years; these data were factor analyzed in two separate joint analyses. A number of analyses were conducted to determine what factors each of the tests have that are unique and what factors they share. “The most crucial finding from these analyses is that the Wechsler Performance subtests and the KAIT Fluid subtests seem to measure markedly different constructs” (Kaufman & Kaufman, 1993, p. 93). According to Horn, there are important differences between Performance IQ and fluid intelligence, noting that Performance IQ “involves visualization to a very considerable extent” (Horn & Hofer, 1992, p. 72). The following conclusions from the joint factor analyses of KAIT and Wechsler subtests were drawn:

Three factors define the joint matrices of the KAIT and the Wechsler scales: Crystallized/ Verbal, Fluid, and Perceptual Organization.

The constructs underlying the KAIT Fluid and the Wechsler Performance Scales are distinctly different. The Fluid and Perceptual Organization factors correlate about as highly with each other as they do with the Crystallized/Verbal factor.

The constructs underlying the KAIT Crystallized the Wechsler Verbal scales seem virtually identical; all component subtests load substantially on the Crystallized/Verbal factor.

The KAIT Crystallized and Fluid subtests load consistently on the factors underlying their respective scales. The Wechsler subtests, however, sometimes do not load highly on the factor underlying the scale to which they belong (Kaufman & Kaufman, 1993).

Critique. The KAIT represents a reconceptualization of the measurement of intelligence that is more consistent with current theories of intellectual development (Brown, 1994). The fluid-crystallized dichotomy, the theory underlying the KAIT, is based on the original Hom-Cattell theory of intelligence, thus offering a firm and well-researched theoretical framework (Flanagan, Alfonso, & Flanagan, 1994). The fluid-crystallized dichotomy enhances the richness of the clinical interpretations that can be drawn from this instrument (Brown, 1994). The test materials are well constructed and attractive, and the manual is well organized and helpful (Dumont & Hagberg, 1994; Flanagan et al., 1994). Furthermore, the test materials are easy to use and stimulating to examinees (Flanagan et al., 1994).

“The KAIT has been standardized by state-of-the-art measurement techniques” (Brown, 1994). The psychometric properties of the KAIT regarding standardization and reliability are excellent and the construct validity evidence that is reported in the manual provides a good foundation for its theoretical underpinnings (Flanagan et al., 1994).

The theoretical assumption that formal operations are reached by early adolescence limits the application of the KAIT with certain adolescent and adult populations (Brown, 1994). If an individual has not achieved formal operations, many of the subtests will be too difficult for them and perhaps frustrating and overwhelming. Examiners should be aware of this when working with such individuals in order to maintain rapport. The KAIT can be a great assessment tool when working with high-functioning, intelligent individuals; however, it can be difficult to use with borderline individuals and some elderly clients. Elderly clients’ scores on some of the subtests may be negatively impacted by poor reading, poor hearing, and poor memory (Dumont & Hagberg, 1994).

Flanagan and colleagues (1994) report that the inclusion of only three subtests per scale may limit or interfere with the calculation of IQs if a subtest is spoiled. The usefulness of the Expanded Battery and Mental Status subtest of clinical populations is questionable given the reliability and validity data presented in the manual, suggesting that interpretations be made with caution (Flanagan et al., 1994).

Although there clearly are some limitations in the use of the KAIT with some populations, overall, the test appears to be well thought out and validated (Dumont & Hagberg, 1994). The KAIT represents an advancement in the field of intellectual assessment with its ability to measure fluid and crystallized intelligence from a theoretical perspective and, at the same time, maintain a solid psychometric quality (Flanagan et al., 1994).

Description

(i) Intelligence Tests

Intelligence tests are among the oldest devices in the psychometric arsenal of the psychologist and are likely the most frequently used category of tests in the evaluation of exceptional children, especially in the cases of mental retardation, learning disabilities, and intellectual giftedness. Intelligence and aptitude tests are used frequently in adult assessment as well and are essential diagnostic tools when examining for the various dementias. They are used with adults in predicting a variety of other cognitive disorders and in the vocational arena. Since the translation and modification of Alfred Binet's intelligence test for French schoolchildren was introduced in the United States by Lewis Terman (of Stanford University, hence the Stanford-Binet Intelligence Scale), a substantial proliferation of such tests has occurred. Many of these tests measure very limited aspects of intelligence (e.g., Peabody Picture Vocabulary Test, Columbia Mental Maturity Scale, Ammons and Ammons Quick Test), whereas others give a much broader view of a person's intellectual skills, measuring general intelligence as well as more specific cognitive skills (e.g., the various Wechsler scales). Unfortunately, while intelligence is a hypothetical psychological construct, most intelligence tests were developed from a primarily empirical basis, with little if any attention given to theories of the human intellect. Empiricism is of major importance in all aspects of psychology, especially psychological testing, but is insufficient in itself. It is important to have a good theory underlying the assessment of any theoretical construct such as intelligence.

Intelligence tests in use today are for the most part individually administered (i.e., a psychologist administers the test to an individual in a closed setting with no other individuals present). For a long time, group intelligence tests were used throughout the public schools and in the military. Group tests of intelligence are used more sparingly today because of their many abuses in the past and the limited amount of information they offer about the individual. There is little of utility to the schools, for example, that can be gleaned from a group intelligence test that cannot be obtained better from group achievement tests. Individual intelligence tests are far more expensive to use but offer considerably more and better information. Much of the additional information, however, comes from having a highly trained observer (the psychologist) interacting with the person for more than an hour in a quite structured setting, with a variety of tasks of varying levels of difficulty. The most widely used individually administered intelligence scales today are the Wechsler scales, the Kaufman scales, and the Stanford-Binet Intelligence Scale (Fourth Edition). Though the oldest and best known of intelligence tests, the Binet has lost much of its popularity and is now a distant third.

Intelligence testing, which can be very useful in clinical and vocational settings, is also a controversial activity, especially with regard to the diagnosis of mild mental retardation among minority cultures in the United States. Used with care and compassion, as a tool toward understanding, such tests can prove invaluable. Used recklessly and with rigidity, they can cause irreparable harm. Extensive technical training is required to master properly the administration of an individual intelligence test (or any individual test for that matter). Even greater sensitivity and training are required to interpret these powerful and controversial devices. Extensive knowledge of statistics, measurement theory, and the existing research literature concerning testing is a prerequisite to using intelligence tests. To use them well requires mastery of the broader field of psychology, especially differential psychology, the psychological science that focuses on the psychological study and analysis of human individual differences and theories of cognitive development. Extensive discussions of the clinical evaluation of intelligence can be found in Kaufman (1990, 1994) and Kaufman and Reynolds (1983).

Issues in Summarizing Overall Ability

The FSIQ has strong explanatory and predictive power at the group and individual level. Still, the use of an overall summary score may mask individual differences among the broad domains of general ability, especially in patients with neuropsychological deficits where the focus of clinical attention is not prediction but diagnosis of underlying cognitive deficits. For this reason, the relevance of reporting IQ scores has been questioned (Fiorello et al., 2007). Yet, other researchers suggest that FSIQ may be an equally valid measure of general ability for individuals or groups having highly variable index scores as for those having consistent index scores (Daniel, 2007) and that there may be no difference in the predictive validity of FSIQ for low-scatter and high-scatter groups (Watkins, Glutting, & Lei, 2007).

FSIQ is an especially strong predictor of educational attainment, occupational level, memory functioning, and school achievement (Wechsler, 2008, 2009). FSIQ and achievement, for example, correlate strongly, typically around 0.70. This means that FSIQ explains about half the variance in achievement. There is no known variable or collection of variables that comes close to fully accounting for the other half. Beyond the relationship with achievement, there is considerable ecological and criterion validity for the use of an overall estimate of general intelligence in a variety of areas related to success in life including pre-employment testing and predicting job performance (Gottfredson, 1997, 1998; Kuncel, Hezlett, & Ones, 2004). Thus, when the focus of clinical attention is prediction then FSIQ is often the most potent predictor. When the focus is clinical diagnosis of pathology then the index scores are often more informative.

Unlike every other Wechsler interpretative system that has been written, we discuss FSIQ last, rather than first. This is not to devalue the explanatory and predictive power of the FSIQ, but to emphasize the descriptive clinical power of the WAIS–IV Indexes and to place FSIQ in its proper role of providing a relevant backdrop against which the index scores are evaluated. This is consistent with our position that the first line of clinical interpretation rests with the index scores.

4.08.3.2 Integration of KAIT with Wechsler Scales

The KAIT was developed from the Horn–Cattell theory and yields both a Crystallized IQ and Fluid IQ. The three subtests comprising the KAIT Fluid Scale are very good supplements to the Wechsler scales. As noted previously, there is controversy regarding how well the Wechsler scales measure fluid abilities; thus, it is wise to administer supplemental tests to tap an individual's fluid reasoning ability and learning ability. Assessment of planning ability, formal operational thought, and learning ability may be obtained through KAIT Fluid Subtests: Mystery Codes and Logical Steps. Problem-solving through verbal reasoning and verbal comprehension is required in Logical Steps, and Rebus Learning demands vocal responding; therefore, the KAIT Fluid Scale measures an ability that is quite different from Wechsler's P-IQ. If questions about an individual's planning speed arise from the primary battery administered, examiners may administer Mystery Codes to further assess planning speed.

To supplement Wechsler's Verbal Scale, the KAIT Crystallized subtests may be used. For assessing an individual's base of general factual knowledge, Famous Faces may be administered to supplement WISC-III or WAIS-R Information. Famous Faces uses pictorial stimuli integrated with verbal clues about famous people; whereas Information is a purely auditory-vocal task. Formal operational thought within the Crystallized domain can be assessed through Double Meanings. Double Meanings challenges examinees to unify apparently disparate semantic stimuli. KAIT subtests, Double Meanings and Definitions, can also provide follow-up to questionable performance on tasks of word knowledge and verbal concept formation, such as Wechsler's Vocabulary or Similarities. Auditory Comprehension can be used for questions regarding an individual's memory and comprehension ability. This subtest mimics a real-life situation, in requiring an individual to listen to a mock news broadcast and answer questions about it. The two delayed recall (TSR) KAIT subtests are also very good WISC-III supplements when hypotheses are raised regarding an individual's memory.

The Culture-Fair Intelligence Test (CFIT)

The CFIT (R. B. Cattell, 1973) is a nonverbal measure of an individual’s intelligence. This assessment instrument is designed to overcome the influences of verbal fluency, cultural background, and educational level. The CFIT is said to be unique in that it was designed to measure fluid abilities, whereas traditional tests stress the measurement of crystallized abilities. Thus, in theory, the CFIT allows an evaluation of the future potential of an individual, rather than assessing past achievements or lack of achievements.

The tests are of paper-and-pencil format and have time limits for each subtest. Scale 1 is intended for children aged 4–8 years and for retarded adults. This particular scale is not considered by the test authors to be group-administered or fully culture-free. Scale 2 is for ages 8 to 13 years, and for average adults, and Scale 3 is for high school students and superior adults. The participant’s total working time is only 12 1/2 minutes, but the total administration time is closer to 30 minutes. The CFIT has been criticized for its lengthy instructions that cause children to lose attention and become bored. Another criticism is that bright adults with learning disabilities, particularly those with left-right reversal difficulties, are said to obtain low scores on this test (Vane & Motta, 1990).

Internal consistency coefficients averaged across samples are: Scale 1, .91; Scale 2, .82; and Scale 3, .85. Test-retest reliabilities are; Scale 1, .80; Scale 2, .84; and Scale 3, .82. The CFIT correlates with other intelligence measures in the mid-.70 range. Despite this, several studies of the CFIT have produced mixed results. For example, it has been shown that there are only moderate correlations from .20 to .50 with scholastic achievement, although predictive validities have been fairly impressive for certain groups and criteria. Moreover, correlations with other intelligence tests are mostly between the .50 to .70 range, suggesting that the test is measuring the “g” factor. The CFIT has been administered to many culturally diverse groups outside of the United States and produces scores that are comparable between groups. Although the tests show somewhat lower correlations with socioeconomic status than culture-loaded or other primarily verbal tests, and some bilingual immigrant groups score higher on these tests than on conventional IQ tests, the CFIT does not greatly reduce the magnitude of score differences when administered to culturally disadvantaged groups.

The Intelligence Quotient

When intelligence test development first started, the intelligence of an individual mostly was described in terms of the mental age or the IQ. The use of this measure allows both the delay and the advantage in mental development to be estimated. The ratio IQ seemed to be a good measure for estimating the intellectual level of young children. For older children and adults, this measure of intelligence appeared less suitable. First, the idea behind Binet's test was that mental development is directly related to age and that progression in mental development automatically leads to better test scores. Of course, mental development is related to age, but the progress in mental development will not be the same each year we become older. Apparently, there is no linear progression in development. Second, a 2-year difference between mental age and chronological age at the age of 5 years is not comparable with a 2-year difference at the age of 9 years. This incongruity is even greater after the chronological age of 15–17 years. At this adolescent age level, we hardly see differences in the mean raw scores of the various age groups.

Therefore, the ratio IQ coefficient appears to be a poor measure of intelligence. For this reason, modern tests all have deviation IQs. By using deviation-IQ scores, it is possible to calculate how much an individual's test score deviates from the mean test score achieved by a representative peer group of this individual. The calculation of the deviation IQ goes as follows: (1) large representative norm groups of people of various ages are tested, (2) the mean raw test scores and standard deviations are calculated, and (3) it is assumed that intelligence test scores for each age group have normal distributions. For the calculation of deviation IQs per age group, the raw test scores are transformed into norm scores. Almost all intelligence test constructors follow the rule that the mean raw test scores for each age group are transformed into the deviation IQ of 100, with a standard deviation of 15. Therefore, 68.3% of all IQ scores lie within the 85–115 IQ score range and more than 95% of all IQ scores lie within the 70–130 IQ score range, as Fig. 1 shows.

By using the deviation IQ, the test scores of each examinee can be compared with those of his or her peer group. Instead of the original comparison of the mental age with the chronological age, with deviation IQs the scores of each individual can be related to the norm tables of his or her age group. Scores on different tests easily can be compared with one another because almost all the different instruments have norm scores with equal means and standard deviations.

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