Handbook of psychology volume 7 educational psychology
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- Definitional Issues 459
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- A Resolution of Definitional Issues
Definitional Issues 457 458 Learning Disabilities composed of two scales—a Verbal Scale in which the ques- tions are largely based on language, from which one calcu- lates a Verbal IQ, and a Performance Scale, from which one calculates a Performance IQ. It is also possible to calculate a total or full-scale IQ score. If a discrepancy between IQ and achievement is used, then which IQ score should be used—the Verbal, Performance, or full-scale score? It is quite possible to be categorized as dyslexic on the basis of one IQ score but not if another IQ score is used. For example, Valtin (1978–1979) found that it makes a difference which scale is used, the Verbal or Performance Scale. Children are often classified as dyslexic when the classification is based on one scale, but they are not considered dyslexic when the decision is based on the other. In addition, depending on the type of IQ scores, the dif- ference between the good and poor readers could be signifi- cant or not significant, depending on which IQ score was used in the definition. There is also empirical evidence that suggests it is not nec- essary to use the concept of intelligence in defining reading disabilities. When children with reading disabilities were di- vided into groups based on their IQ level and compared on a variety of reading, language, memory, spelling, and phono- logical tasks, there were no differences between the IQ groups on the reading-related tasks (Siegel, 1988b). There- fore, the reading-disabled group was quite homogeneous in relation to reading-related skills; administering an IQ would not provide useful information about performance differ- ences on reading-related tasks. One typical use of the IQ test is to use the IQ score to mea- sure the discrepancy between IQ and academic achievement. If there is a discrepancy, then the individual is said to have a learning disability. If the individuals are poor readers but show no discrepancy between their IQ and reading scores, then they are not considered reading disabled. Fletcher et al. (1989) maintains that it has not been clearly demonstrated that children with discrepancies in IQ and achievement have more specific disabilities than do poor achievers whose IQ scores were not discrepant. In fact, they contend that there is relatively little empirical evidence to show that similarly de- fined children differ on measures other than IQ. In an epi- demiological study on the influence of various definitions of learning disabilities on the selection of children, Shaywitz, Shaywitz, Barnes, and Fletcher (1986) found that although variations in the use of IQ indexes led to the identification of different children as learning disabled, there were few dif- ferences in cognitive abilities. Moreover, there were few differences among identified LD children with discrepant and nondiscrepant IQ scores. A significant number of studies have found no difference in the reading, spelling, phonological skills, and even reading comprehension of learning disabled individuals with high and low IQ scores and no differences between individuals with dyslexia and poor readers on measures of the processes most directly related to reading (e.g., N. Ellis & Large, 1987; Felton & Wood, 1991; Fletcher, Francis, Rourke, Shaywitz, & Shaywitz, 1992; Fletcher et al., 1994; Friedman & Stevenson, 1988; Gottardo, Stanovich, & Siegel, 1996; Hall, Wilson, Humphreys, Tinzmann, & Bowyer, 1983; Jiménez-Glez & Rodrigo-López, 1994; Johnston, Rugg, & Scott, 1987a, 1987b; Jorm, Share, Matthews, & Maclean, 1986; Share, McGee, McKenzie, Williams, & Silva, 1987; Siegel, 1988b, 1992, 1998; Silva, McGee, & Williams, 1985; Stanovich & Siegel, 1994; Taylor, Satz, & Friel, 1979; Toth & Siegel, 1994). For example, Siegel (1992) compared two groups of children who had low reading scores. One group, which was composed of individuals with dyslexia, had reading scores that were significantly lower than were those that were pre- dicted by their IQ scores; the other group, the poor readers, had low reading scores, but these reading scores were not sig- nificantly lower than would be predicted by their IQ scores. On a variety of reading, spelling, and phonological tasks, results showed no differences between these two groups in reading comprehension. In other words, there is no need to use IQ scores to predict the difference between the individu- als traditionally called learning disabled and those who have equally poor achievement but also have lower IQ scores. These results have also been replicated in a study of adults with reading disabilities (Siegel, 1998). These findings sug- gest that there is no need to use IQ tests to determine who is learning disabled. We need to use only achievement tests. In addition, IQ scores do not predict who is able to benefit from remediation (Arnold, Smeltzer, & Barneby, 1981; Kershner, 1990; Lytton, 1967; Van der Wissel & Zegers, 1985; Vellutino & Scanlon, 1996; Vellutino, Scanlon, & Lyon, 2000). One study (Yule, 1973) found that reading disabled children with lower IQ scores made more gains than did read- ing disabled children with higher scores. Other research shows that reading problems may actually interfere with the development of language, knowledge, and vocabulary skills, further complicating the issue of the rela- tionship between IQ and reading; this is called the Matthew effect. The Matthew effect refers to the bidirectional relation- ship between reading and cognitive development. Stanovich (1986, 1988a, 1988b) has conceptualized the Matthew effect as “the tendency of reading itself to cause further develop- ment in other related cognitive abilities”—that is, IQ—such that the “rich get richer and [the] poor get poorer” (Stanovich, 1986, p. 360). Certain minimum cognitive capabilities must be present to begin reading; however, after reading com- mences, the act of reading itself further develops these same
Definitional Issues 459 cognitive capabilities; this relationship of mutual reinforce- ment is called the Matthew effect. This Matthew effect of a reciprocal relationship between reading and other cognitive skills is reflected in performance on an IQ test; consequently, it undermines the validity of using an IQ-discrepancy-based criterion because children who read more gain the cognitive skills and information relevant to the IQ test and thus attain higher IQ scores. Children with reading problems read less; therefore, they fail to gain the skills and information neces- sary for higher scores on the IQ test. If the Matthew effect as described by Stanovich were operating, it would be expected that IQ scores would decline with increasing age because vocabulary and knowledge in- crease as a result—at least in part—of experiences with print. If reading disabled children have less experience with print than do children without reading problems, then the chance to acquire new knowledge is reduced and the IQ scores are expected to decrease over time. In a cross-sectional study, Siegel and Himel (1998) found that the IQ scores—in partic- ular, vocabulary scores—of older dyslexic children were significantly lower than were those of younger dyslexic chil- dren. Similar declines in IQ and vocabulary were not noted for the normally achieving readers—that is, children who showed age-appropriate reading skills. However, standard scores of the children with reading problems compared to chronologically age-matched children remained relatively constant with time, so that there was not an overall decline in skills. Scores on a subtest of the IQ test, Block Design, a test of visuospatial as opposed to verbal skills, also remained constant over time. This subtest measures visuospatial skills more than it does verbal skills, and it is not directly related to the knowledge required by reading. In addition, younger children were much more likely to be classified as dyslexic (as opposed to poor readers) than were older children because of the so-called decline in IQ scores that resulted from lack of print exposure. Finally, if intelligence is a measure of some stable construct of ability or potential and IQ tests measure it, then these test results should be stable over time. Elliot and Boeve (1987) found that the variable time has a statistically significant effect on both children’s WISC-R verbal and per- formance scores. Therefore, for these students, it is question- able if the WISC-R is measuring a stable construct. Ultimately, services may be denied to individuals who have not been administered an IQ test or who do not achieve a certain score on the IQ test (e.g., see Padget, Knight, & Sawyer, 1996). IQ scores are significantly correlated with socioeconomic status—that is, children from lower socioeco- nomic backgrounds are likely to have lower IQ scores probably because of a relative lack of experience with the vo- cabulary and knowledge measured by the IQ test. Children from low socioeconomic backgrounds are more likely to be classified as poor readers than are dyslexics even though these children have the same degree of reading difficulty as dyslexics (Siegel & Himel, 1998); this means that the use of the discrepancy definition discriminates against children from low-SES backgrounds. Some argue that we should use IQ test scores because IQ is correlated with achievement (e.g., Wong, 1996). As Tunmer (1989) has noted, parental income is correlated with reading achievement (the correla- tions are almost identical in magnitude to those between reading and IQ); why not use a discrepancy between parental income and reading achievement as a measure of dyslexia? A significant discrepancy would be needed for the individual to get remedial help. The social consequences and unfairness of this suggestion are obvious, but the principle is the same as using a discrepancy between IQ and achievement. The requirement for the use of the IQ score provides us with the dilemma of determining an IQ score that is neces- sary for an individual to achieve to be considered learning disabled. Some studies use 80, others 85, others 90, and some even use 100. For example, although they recognize that there are problems with the use of IQ in the identification of learning disabilities, Padget et al. (1996) argue that Clinical judgment may be needed when considering cases in which the Verbal IQ is below 90. Two cases in which this may be particularly important are older students who previously achieved a Verbal IQ above 90 and students who have low sub- test scores only on the subtests that require significant auditory, sequential memory skills to perform the task. In most other cases when students score below these guidelines it strongly suggests that reading problems may be related to factors other than, or in addition to, dyslexia. (p. 59). However, they present no evidence for this assertion. An opposing conclusion has been reached by G. Reid Lyon (1995) of the U.S. National Institute of Child Health and Human Development as follows: The assumption that a discrepancy between achievement and aptitude (typically assessed using intelligence tests) is a clear diagnostic marker for learning disabilities or can be considered a pathognomonic sign is at best premature, and at worst invalid. (p. 5121) Often, it is recommended that instead of the IQ test, mea- sures of listening comprehension be used presumably because this will assess an individual’s level of cognitive processing (Aaron, 1991; Padget et al., 1996). Listening comprehension measures typically consist of the examiner’s reading aloud a passage to the individual and then asking him or her questions 460 Learning Disabilities about the text. This type of task places heavy demands on memory, and if an individual fails to answer a question cor- rectly, the examiner does not know whether the individual did not understand the passage or has merely forgotten the an- swer. Ability to remember what has been heard also depends on one’s background knowledge of the material in the text. Unlike when one reads text in which the material is available, one cannot refer back to the material in a listening compre- hension task. Therefore, the time has come to abandon listen- ing comprehension as an alternative to the IQ test. Another assumption of many LD definitions—including US Public Law 94-142, Ontario’s Bill 82, and the NJCLD’s definition—is that there must be a discrepancy between IQ and achievement. In other words, the child’s achievement is not commensurate with his or her ability or intelligence (IQ). The second assumption of the discrepancy definition is that measures of intelligence and measures of achievement are independent. This assumption has been questioned by some investigators (see Lyon, 1987, for a complete discus- sion), but I maintain that it is necessary if a discrepancy defi- nition is to be meaningful. If one accepts the argument that intelligence is not orthogonal to achievement, then there would be no reason to expect a discrepancy. Therefore, a dis- crepancy definition is logical if and only if the presence of a learning disability does not affect IQ test scores but does affect achievement test scores. Then children with LD would have a discrepancy between the scores on their IQ tests and the scores on their achievement tests, whereas normally achieving children and those with other disabilities will have scores on these tests that are similar (not discrepant). A number of investigators (Green, 1974; Hopkins & Stanley, 1981; Siegel, 1988a, 1988b) have suggested that this assumption of independence is questionable. Green (1974) argues, for example, that comparisons of scores for ability and achievement are meaningful only to the extent to which unique elements are measured. Hopkins and Stanley (1981) examined the overlapping variance in a well-constructed intelligence test (the Lorge- Thorndike) and in two subtests (the reading and the arith- metic) of a well-constructed achievement test (the Iowa Test of Basic Skills). On average, 47% of the variance was found to overlap. This finding suggests that when one ability test and one achievement test are used, about 50% of the time the same concept is being measured; this clearly violates the assump- tion of independence among concepts measured by the ability and achievement tests. It can only be hoped that the other 50% of the variance is tapping something different that can provide insight to the true differences revealed by the comparison. Discrepancy definitions also have been questioned on sta- tistical grounds. Reynolds (1984–1985, 1985) notes that many discrepancy models are based on grade equivalents. He points out that these models have problems in two areas. First, nei- ther age nor grade-equivalent scores provide adequate mathe- matical properties (cannot be added, subtracted, multiplied, or divided) for use in discrepancy analysis. Second, the amount of retardation reflected by 2 years below grade level changes with increasing grade level. A much greater level of retarda- tion is reflected by a 2-year deficit at Grade 2 than at Grade 7, and even less retardation would be reflected at Grade 11. Therefore, a much greater deficit would be needed for a child in Grade 3 to be identified as LD than for one in Grade 10. In summary, the weight of the evidence leads us to con- clude that IQ scores are irrelevant to the definitions of learn- ing disabilities.
There are two types of specificity: The first involves the degree to which the individual’s problem is specific to one or more cognitive areas, and the second involves the issue of whether all children with learning disabilities should be considered one homogeneous group.Anumber of authors (Hall & Humphreys, 1982; Stanovich, 1986, 1988a; Swanson, 1988b, 1989) have maintained that one of the essential concepts of a learning dis- ability is its specificity—that is, a learning disability is pre- sumed to be caused by a neurological inefficiency that affects a narrow group of subskills of cognitive processes; this affects a specific domain of academic skills but leaves intellectually ability intact. In other words, a learning disability reflects a cognitive deficit possibly due to a neurological dysfunction that is comparatively specific to a particular domain (e.g., reading or arithmetic). Swanson (1988a) has suggested that these specific deficits must not stray too far into other cogni- tive domains, or the concept of a specific learning disability will blend with other more generalized conditions (e.g., men- tal retardation). As well, Stanovich (1986) maintains that def- initions of dyslexia must rest on an assumption of specificity. He contends that dyslexia results from a brain or cognitive deficit that is reasonably specific to reading. Siegel (1988a) and Bryant and Brown (1985) argue that this type of specificity is unrealistic. Siegel (1988a) maintains that if children have problems in working memory, this con- dition could affect a variety of academic tasks—especially in areas such as reading, spelling, and arithmetic. Brown and Bryant (1985) suggest that if a child has a severe language problem, this condition could influence a large number of cog- nitive areas: reading, writing, speaking, listening, or any com- bination. Moreover, Siegel (1988a) contends that implicit in the specificity assumption is the assumption that domains such as reading and arithmetic are entirely independent cognitive Definitional Issues 461 processes. This assumption is invalid because working mem- ory and recognizing and labeling abstract symbols are involved in both reading and arithmetic skills, and a child who has difficulty with these cognitive processes is likely to have problems with tasks involving such skills (Siegel, 1988a). The second type of specificity involves questions about the degree to which all children with LD have the same problems or whether there are subtypes. On the basis of what is now known, the concept of a generalized homogeneous group la- beled LD children should be abandoned; the child with LD should be considered as part of a smaller, more clearly de- fined subtype (Siegel, 1988a). As well, other theorists (e.g., Bateman, 1968–1969; Benton & Pearl, 1978; Boder, 1973; Kinsbourne & Warrington, 1963; Rourke, 1983, 1985) have contended that differences within the population of children with learning disabilities may reflect the existence of distin- guishable subtypes. In other words, not all learning-disabled children have the same types of disabilities, and independent subtypes include distinctive characteristics and antecedent conditions that consistently predict specific patterns of learn- ing difficulties. Therefore, failure to differentiate among types of learning disabilities can lead to inaccurate conclu- sions. For example, Siegel and Ryan (1984, 1988) found that children with reading disabilities have difficulty processing certain aspects of syntax, whereas specific children with specific arithmetic disabilities (and no reading disability) do not. Differences between the same two groups have been found in working memory (Fletcher, 1985; Siegel & Linder, 1984; Siegel & Ryan, 1989a). Swanson (1988b) found that children with a reading disability may be characterized by different patterns of memory dysfunction. These differ- ences are reflected on measures of achievement in reading and arithmetic. If all these children had been considered to- gether as a homogeneous group, these differences might have been obscured.
Clearly the field of special education continues to have prob- lems defining and classifying children with learning disabili- ties. Current discrepancy definitions are problematic and should be reconsidered because they cannot be justified in light of their illogical nature. But where does that leave us and where can we go from there? One way in which meaning is given to a concept is by defining it operationally. Specifically, an operational defini- tion explains a concept solely in terms of the operations used to produce and measure it. Recognizing that there are prob- lems inherent in operational definitions (e.g., the meaning of the concept is restricted to the narrowly described operations used for measuring it), I suggest that learning disabilities (a) need to have an IQ threshold because I recognize that the field is not ready to accept Siegel’s (1989a, 1989b) challenge to the use of IQ tests; (b) should refer to a significant diffi- culty in a school-related area; and (c) should exclude only severe emotional disorders, second-language background, sensory disabilities, and specific neurological deficits. Evidence (Siegel, Levey, & Ferris, 1985; Siegel & Ryan, 1989b) suggests that the type of operational definition used for the concept may influence the outcome and conclusions of the study. Siegel and Ryan (1989b) have argued that the actual de- finition used for a reading disability can make a difference in the conclusions that are drawn about information-processing characteristics of the children and whether there are reading- disability subtypes. In one study, poor readers (all with IQ scores equal to or above 80) were divided into four groups as follows: (a) those with deficits in phonological processing— inadequate phonological skills based on the reading of pseu- dowords, (b) those with word-recognition deficits, (c) those with comprehension-only deficits—inadequate reading com- prehension skills but adequate word-recognition skills, and (d) those with rate-only deficits—slow reading speed but ade- quate word-recognition skills. When each disabled group was compared to an age-matched normally achieving group, dis- tinct cognitive differences appeared. For example, children with a phonological deficit or a word-recognition deficit had scores that were significantly lower than were those of normal readers on short-term memory tasks but not on language tasks. The readers with rate-only deficits had cognitive pro- files similar to those of normally achieving children. There- fore, the children with word-recognition problems are probably the ones with language deficits and those with only a reading comprehension problem probably do not have lan- guage problems. In addition, there was approximately a 25% overlap be- tween poor comprehenders and poor readers; therefore, had a reading comprehension test been used to define the learning- disabled group and word recognition not been used as a con- trol, the reading-disabled group would have consisted of some children with word-recognition problems and some without. This leads to the question How should a reading disability be defined? Stanovich (1986, 1989) has suggested that the core deficits in a reading disability are problems in phonolog- ical processing. Although reading is more than simply decod- ing and recognizing words (one has to remember what was read, put it into context, etc.), unfortunately currently there are no accurate tests to measure these variables (see Siegel & Heaven, 1986, for a complete discussion of this issue). Further empirical evidence suggests that when a difficulty |
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