ADHD and reading disabilities: a cluster analytic approach for distinguishing subgroups

Data suggest that children with reading disability (RD) and non-RD children with attention-deficit/hyperactivity disorder (ADHD) may comprise distinct subgroups. Research has been hampered by variance in definitional criteria, which results in the study of different subgroups of children. Using cluster analysis, this study empirically divided children with ADHD (N = 54), based on their Full Scale IQ (FSIQ) and reading ability. Four distinct subgroups emerged in which cognitive, behavioral, and neurochemical function was compared. Cluster 1 was of average FSIQ and reading scores; Cluster 2 was of average FSIQ but showed impairment in reading; Cluster 3 had high FSIQ and reading scores; and Cluster 4 had low scores in both domains. The groups had different patterns of cognitive, behavioral, and neurochemical function, as determined by discrepancies in Verbal-Performance IQ, academic achievement scores, parent aggression ratings, and a measure of noradrenergic function. These distinctions are discussed with regard to etiology, treatment, and long-term outcome.     

Tourette syndrome and learning disabilities.

We reviewed the records of 42 consecutive cases of children with Tourette Syndrome (TS) who had IQs above 70, and contrasted the reading, reading comprehension, math, and spelling quotients with IQ scores to determine how many would meet criteria for a learning disability. The mean IQ of the 35 males and 7 females was 94.4 and was higher than the mean math score (82.8), spelling score (90.4), reading score (87.4), and reading comprehension score (85.3). Using a 1.5 standard deviation discrepancy, 51% met criteria for learning disability in at least one academic area; 21% had a 2-standard-deviation discrepancy. Children with TS frequently have learning disabilities, and assessment of academic achievement should be a routine aspect in the evaluation of such children.     

Attention deficit disorder and specific reading disability: separate but often overlapping disorders

Within a large (N = 182) heterogeneous sample of clinic-referred children with DSM-III-diagnosed attention deficit disorder (ADD), three behavioral subgroups were identified via cluster analysis of teacher ratings: 40% of the children had ADD with hyperactivity (ADDH), 30% had ADD with hyperactivity and aggressivity (ADDHA), and 31% had ADD without hyperactivity or aggressivity. Proportionally more girls were in the ADD-only subgroup. Over half the sample (n = 94) were poor readers, with 82 meeting discrepancy criteria for specific reading disability (RD). Proportionately more boys than girls met the RD criteria (9.2:1.0), whereas the sex ratio of males to females for the whole sample was 5.1 to 1.0. Focusing just on white males, the three behavioral subgroups were significantly different on convergent validity measures, such as other teacher ratings, parent ratings, and interview-elicited ratings of externalizing behavior, but were not different on such divergent validity measures as IQ and achievement scores, self-ratings, and laboratory performance tasks. Boys in the ADD sample who did not meet criteria for RD had significantly higher IQs than those who did, but subgroups with and without RD still differed significantly on WRAT-R reading and spelling scores with IQ covaried out. Both groups with and without RD could be differentiated from a control group on laboratory measures of sustained attention and impulse control. Methylphenidate benefited all subgroups equally, whether RD or not, and whether given a low (0.3 mg/kg) or high (0.6 mg/kg) dose.     

Gender bias in IQ-discrepancy and post-discrepancy definitions of reading disability

The present study investigated the hypothesis that the higher prevalence of reading disability (RD) often observed among boys is partly an artifact of gender bias in the prediction of reading from IQ. The relevant regression statistics derived from a sample of more than 900 children revealed a statistically significant intercept bias. Predicted reading scores for boys were systematically overestimated, thereby inflating IQ-reading discrepancies; the converse was found for girls. When defined separately for girls and boys, severe underachievement in reading was found to be equally prevalent in both genders and, furthermore, was associated with qualitatively and quantitatively similar patterns of deficits. Because the bias arose from general differences between boys and girls in reading score distributions (a lower mean and greater variance for boys) rather than from differences in IQ scores, gender bias poses a potential threat not only to traditional IQ-discrepancy definitions but also to post-discrepancy definitions that are based solely on reading score cutoffs. Future classification criteria for RD need to take heed of the possibility that when the distributions of reading scores for boys and girls are not identical, performance cutoffs designating low achievement that are based on data pooled from both genders are likely to result in the overidentification of boys with RD and the underidentification of girls with RD.     

Persistent arithmetic, reading, or arithmetic and reading disability

The achievement of 1,075 school children was followed to the end of grade 7 or 8. Retrospective details of birth, medical history, and infant adaptive behavior, as well as current information about preschool behavior, were provided by parents before kindergarten entry when their children were ages four to five. At that time, each child was given language, preacademic, and visual-motor tests, and a short-form verbal IQ was obtained. For grades 1 to 8, a mean 6.9 percent qualified as low in arithmetic (including 3.9 percent low only in arithmetic) and 9 percent as low in reading (including 6 percent low only in reading). Groups of children with persistent disability in arithmetic only (2.3 percent), reading only (6.6 percent), and arithmetic plus reading (3.4 percent) were compared on all variables, and gender differences were examined. The specific arithmetic group was superior to the other two groups in preschool verbal IQ and language, and had suffered more birth problems and illness. As found by Rourke and his colleagues (e.g., Rourke and Finlayson 1978) for older children, boys with a specific arithmetic disability showed a preschool profile with high verbal scores and low nonverbal scores. Many gender differences were found for the total sample, but few for the learning disability subgroups.     

Comparisons of cutoff and regression-based definitions of reading disabilities

This study addressed the issue of specificity in reading disability by comparing two approaches to defining and selecting children with reading disabilities. One approach defined reading disability according to cutoff scores representing appropriate levels of intelligence and reading deficiency, whereas the other approach adjusted these scores for their intercorrelation through regression procedures. Results revealed clear differences in which children were identified as reading disabled according to the two definitions. However, differences in neuropsychological performance between children whose reading scores were discrepant or not discrepant with IQ were small and nonspecific for both definitions. The results of this study show that children identified as reading disabled vary according to the definition employed; at this point, there is little evidence suggesting any specificity of reading disability according to definition.     

How Should Reading Disabilities be Operationalized? A Survey of Experts

In the face of accumulating research and logic, the use of a discrepancy between intelligence and reading achievement test scores is becoming increasingly untenable as a marker of reading disabilities. However, it is not clear what criteria might replace the discrepancy requirement. We surveyed 218 members of journal editorial boards to solicit their opinions on current and proposed definitional components and exclusion criteria. Three components were selected by over two‐thirds of the respondents: reading achievement, phonemic awareness, and treatment validity. However, only 30 percent believed IQ‐reading achievement discrepancy should be a marker. More than 75 percent of the respondents believed exclusion criteria should remain part of the definition. Mental retardation was the most frequently selected exclusion criterion despite rejection of intelligence test scores as a definitional component. Although the findings reflect uncertainty among experts on what elements should comprise a definition, they do signal a willingness to consider new approaches to the conceptually difficult task of defining reading disabilities.     

Correlates of Academic Overachievement,Nondiscrepant Achievement,and Learning Disability in ADHD,Autism, and General Population Samples

ABSTRACT

Little is known about the characteristics of academic overachievers, children whose achievement significantly exceeds IQ. Correlates of overachievement (achievement test scores ≥ 1 SD above IQ), nondiscrepant achievement, and learning disability (LD; achievement ≥ 1 SD below IQ) were analyzed in 1,543 children (739 ADHD, 285 autism, and 519 general population), 6–16 years of age. Significant correlates of the reading and math achievement groups were diagnosis (autism greatest overachievement, ADHD greatest LD), IQ (lowest in overachievers and highest in LD), and Working Memory scores relative to the child’s IQ (close to or exceeding IQ in overachievers and lower than IQ in LD). Demographics (age, sex, race, and parent occupation) and parent and teacher ratings of psychopathology (e.g., behavior problems, anxiety, and depression) and personality characteristics (e.g., motivation and self-confidence) did not contribute significantly more to predicting overachievement and LD beyond that explained by IQ, diagnosis, and working memory. These findings suggest an underlying neurobiological etiology for both overachievement and LD.     

Do the effects of computer-assisted practice differ for children with reading disabilities with and without IQ-achievement discrepancy?

This study was designed to assess whether the effects of computer-assisted practice on visual word recognition differed for children with reading disabilities (RD) with or without aptitude-achievement discrepancy. A sample of 73 Spanish children with low reading performance was selected using the discrepancy method, based on a standard score comparison (i.e., the difference between IQ and achievement standard scores). The sample was classified into three groups: (1) a group of 14 children with dyslexia (age M = 103.85 months; SD = 8.45) who received computer-based reading practice; (2) a group of 31 "garden-variety" (GV) poor readers (age M = 107.06 months; SD = 6.75) who received the same type of instruction; and (3) a group of 28 children with low reading performance (age M = 103.33 months; SD = 9.04) who did not receive computer-assisted practice. Children were pre- and posttested in word recognition, reading comprehension, phonological awareness, and visual and phonological tasks. The results indicated that both computer-assisted intervention groups showed improved word recognition compared to the control group. Nevertheless, children with dyslexia had more difficulties than GV poor readers during computer-based word reading under conditions that required extensive phonological computation, because their performance was more affected by low-frequency words and long words. In conclusion, we did not find empirical evidence in favor of the IQ-achievement discrepancy definition of reading disability, because IQ did not differentially predict treatment outcomes.     

Reading research for students with LD: a meta-analysis of intervention outcomes

The present article provides a meta-analysis of instructional research with samples of children and adolescents with learning disabilities in the domains of word recognition and reading comprehension. The results of the synthesis showed that a prototypical intervention study has an effect size (ES) of .59 for word recognition and .72 for reading comprehension. Four important findings emerged from the synthesis: (a) Effect sizes for measures of comprehension were higher when studies included derivatives of both cognitive and direct instruction, whereas effect sizes were higher for word recognition when studies included direct instruction; (b) effect sizes related to reading comprehension were more susceptible to methodological variation than studies of word recognition; (c) the magnitude of ES for word recognition studies was significantly related to samples defined by cutoff scores (IQ > 85 and reading < 25th percentile), whereas the magnitude of ES for reading comprehension studies was sensitive to discrepancies between IQ and reading when compared to competing definitional criteria; and (d) instructional components related to word segmentation did not enter significantly into a weighted least square hierarchical regression analysis for predicting ES estimates of word recognition beyond an instructional core model, whereas small-group interactive instruction and strategy cuing contributed significant variance beyond a core model to ES estimates of reading comprehension. Implications related to definition and instructional components that optimize the magnitude of outcomes are discussed.     

The relationship between IQ and reading disabilities in English-speaking Canadian and Spanish children

This study was designed to examine the role of intelligence (IQ) in the definition of reading disabilities (RD) in languages with different orthographic systems. A sample of 94 Spanish children and 157 English-speaking Canadian children with RD was classified into four groups on the basis of IQ scores from the Wechsler Intelligence Scale for Children-Revised (< 80; 81-90; 91-109; 110-140). We examined the reading and spelling skills of Canadian and Spanish children as a function of Full Scale, Verbal, and Performance IQ scores. Significant differences between the languages were found when reading performance was analyzed as a function of Verbal IQ scores, in that there were some differences between the groups of Canadian children with RD but not between the groups of Spanish children. The Canadian children with Verbal IQ scores < 80 demonstrated relatively lower performance in reading and spelling skills than the Canadian groups with higher IQ scores. There were differences in reading tasks as a function of Performance IQ in English but not in Spanish. The differences in the role of IQ as a function of orthographic systems may relate to the greater significance of visual-orthographic as opposed to phonological processing in English.     

The relative roles of IQ and cognitive processes in reading disability

The purpose of the present study was to explore the relative roles of IQ and cognitive processes in reading performance. A sample of 443 Spanish children (264 male, 179 female) ranging in age from 7 to 13 years were classified into four groups according to IQ scores (<80, 80–90, 90–110, >110) and reading disabled (RD) and normally achieving readers (NR) were compared. The findings indicate that IQ scores were not related to the differences between children with RD and NR. We found that reading‐related cognitive deficits do differentiate between RD and NR children. Therefore, IQ scores do not make a significant contribution to our understanding of reading disability.     

Neurobehavioral factors associated with referral for learning problems in a community sample: evidence for an adaptational model for learning disorders

We evaluated community general education (CGE; n = 178), community special education (CSE; n = 30) and hospital-referred (HR, n = 145) children (ages 7-6 to 11-11) prospectively over a 2-year period. During this period, 17 CGE children were referred for evaluation (community referred; CR). Prior to referral, CR children performed more poorly than community-nonreferred (CNR) children on cognitive ability, academic achievement, attention problems, and information processing. CR group performance was equivalent to that of CSE and HR groups, but HR children showed poorer academic achievement. Referred children performed more poorly on all measures than nonreferred, whether they met formal diagnostic criteria for a learning disorder or not. Learning disorders may be better conceptualized as a context-dependent problem of functional adaptation than as a disability analogous to physical disabilities, raising questions about the validity of using psychometric test scores as the criterion for identification.     

Matthew effects in children with learning disabilities: Development of reading,IQ, and psychosocial problems from grade 2 to grade 8

Reading achievement, IQ, and behavior problems were assessed in second and eighth grade for a longitudinal sample of 57 children. Changes in these scores over time were compared for children with no learning disabilities versus children with math or reading disabilities (research-identified and/or school-identified). A widening of the group difference in IQ was seen between the math disabled and nondisabled groups, but otherwise the gaps between groups remained unchanged or narrowed over the six-year interval, indicating that hypothesized negative consequences of initial academic difficulties (“Matthew effects”) did not occur for most of the children with learning disabilities. Elevated rates of behavior problems were seen only for the group with math disabilities, suggesting that the type of learning disability needs to be taken into account in research on the association between academic and psychosocial problems.     

Cognitive functioning as measured by the WISC-R: do children with learning disabilities have distinctive patterns of performance?

Patterns of performance on the Wechsler Intelligence Scale for Children-Revised (WISC-R) have been proposed as useful tools for the identification of children with learning disabilities (LD). However, most of the studies of WISC-R patterns in children with LD have been plagued by the lack of a typically achieving comparison group, by failure to measure individual patterns, and by the lack of a precise definition of LD. In an attempt to address these flaws and to assess the presence of patterns of performance on the WISC-R, we examined data from 121 children with typical achievement (TA), 143 children with reading disabilities (RD), and 100 children with a specific arithmetic disability (AD), ages 6 to 16 years. The results indicated that the RD and AD groups had significantly lower scores than the TA group on all the Verbal IQ subtests. Many of the children with AD and RD showed a significant difference between Verbal and Performance IQ scores, but so did many of the typically achieving children. Although there were some children with LD who showed the predicted patterns, typically, 65% or more of the children with LD did not. Furthermore, a proportion of the TA group-generally not significantly smaller than that of the RD and AD groups-showed discrepancy patterns as well. Our results indicate that the patterns of performance on intelligence tests are not reliable enough for the diagnosis of LD in individual children. Therefore, it might be more profitable to base the detection of an individual's LD on patterns of achievement test scores.     

Growth in Precursor and Reading‐Related Skills: Do Low‐Achieving and IQ‐Discrepant Readers Develop Differently?

Poor readers who met low achievement and IQ‐discrepancy definitions of reading disability were compared with nonimpaired readers on their development of eight precursor and reading‐related skills to evaluate developmental differences prior to students’ identification as reading disabled. Results indicated no evidence for differences between the two groups of poor readers in the development of the eight skills, with three exceptions. Students in the IQ‐discrepant group demonstrated greater growth in letter sound knowledge, greater mean performance in visual‐motor integration at the beginning of first grade, and greater deceleration in rapid naming of letters. When compared to the nonimpaired group, low‐achieving readers demonstrated poorer performance and development in all skills, while the IQ‐discrepant readers demonstrated poorer performance and development in phonemic awareness, rapid naming of letters and objects, spelling, and word reading. The largely null results for comparisons between the two groups of poor readers challenges the validity of the two‐group classification of reading disabilities based on IQ‐discrepancy.     

Rapid Naming and Phonemic Awareness: Contributions to Reading,Spelling, and Orthographic Knowledge

The double-deficit hypothesis suggests that deficient skills on two dimensions, rapid naming and phonemic awareness, are associated with poor reading. We studied the reading, spelling, and orthographic skills of Grade 3 children who met our criteria for double asset (DA), single phonological deficit (PD), single naming speed deficit (NSD), and double deficit (DD) groups. Analyses of variance revealed main effects of each factor, oftentimes modified by significant interactions, on the varied achievement measures. All deficit groups performed below the DA children. Compared to children with NSD, children with PD (a) were less accurate decoders, (b) were faster readers, (c) had weaker spelling dictation, and (d) had comparably poor spelling recognition scores. Children with DD showed a mixed pattern of stronger, equal, or weaker skills compared to younger reading level controls.     

Is there a thing called dyslexia?

A controversy whether developmental dyslexia is qualitatively different from other forms of reading disability has existed among reading specialists for many years because poor readers, regardless of the labels attached to them, resemble each other symptomatically (i.e., in reading achievement). For this reason, it is difficult to establish a priori criteria based on symptoms to identify dyslexia and compare it with other forms of reading disability. One possible solution to this impasse is to see if poor readers differ in the etiology of their reading disability and, if they do, then to see whether one group of poor readers fits the traditional definition of dyslexia. This strategy was adopted in the present study. In this paper, it was hypothesized that the etiology of dyslexia is different from that of other forms of reading disability because there is a difference in the components that malfunction in dyslexia and other forms of reading disability. Studies have shown that the two components that account for a large proportion of variance in reading are decoding and comprehension. Previous studies also indicate that dyslexic children are deficient in decoding skills but not necessarily in comprehension. In this study, reading-disabled children were divided into two groups on the basis of their listening comprehension. Children whose listening comprehension was at or above grade level were placed in one group; poor readers with below-grade-level listening comprehension were placed in the second group. Both groups, however, were matched for reading comprehension. The two groups and a control group of normal readers were administered a number of tasks that were designed to assess the efficiency of the components of reading. It was found that poor readers with normal listening comprehension were deficient in tasks that involved grapheme-phoneme conversion (Component I, decoding). When tested on tasks that minimized decoding requirements, their reading comprehension was comparable to that of normal readers. In contrast, the group with sub-average listening comprehension was poor in measures of reading comprehension, even when decoding requirements were minimal. With the exception of very few children, this group also had adequate decoding skills. Because poor readers with normal listening comprehension had average or above average IQ, they conform to the traditional definition of dyslexia. Poor readers with below average listening comprehension had below average IQ and could be considered as “general reading backward.” It was, therefore, concluded that the etiology of developmental dyslexia is different from that of general reading backwardness. In this paper, the termetiology refers to proximal causal factors such as decoding and comprehension and not to distal causal factors such as genetic and neurological characteristics.     

A longitudinal study of the predictive validity of the system of multicultural pluralstic assessment (SOMPA)

The System of Multicultural Pluralistic Assessment (SOMPA) was initially administered to 700 Anglo, 700 Black, and 700 Hispanic children in California elementary schools in order to develop a nonbiased testing program. Ten years later, 1184 of the original 2100 youths were again tested with the SOMPA in high school. At that time, academic achievement and parental interview data also were collected. The results indicate that: (a) Mean achievement test scores and GPAs for the high school students showed that Anglos obtained higher scores than Hispanics, who received higher scores than Blacks. (b) Among the various medical measures, the Bender Gestalt, Fine Motor Sequencing and Finger-Tongue Dexterity tests of the SOMPA were the only ones able to consistently differentiate between youth who did poorly and those who did well academically ten years after their initial testing. (c) Scores on the 1972 IQ test (WISC-R) showed moderate correlations with achievement test scores ten years later. (d) 1972 IQ scores showed low but reliable correlations with GPAs ten years later. (e) In only a very few instances were IQ correlations with achievement test scores higher for minorities than for Anglos. (f) IQ correlated less well with GPA than with achievement test scores for all three ethnic groups. (g) An adjusted IQ, called Estimated Learning Potential (ELP), was more predictive of school achievement than was verbal IQ, particularly for Blacks in the lowest sociocultural quartile. (h) In the second lowest sociocultural quartile, the VIQ correlations with academic measures were reliably higher than the VIQ-ELP correlations, but only for the Anglo and total groups. (i) In the upper two sociocultural quartiles, for all ethnic groups combined, VIQ correlated slightly, but significantly, higher than ELP with school achievement. (j) Also in the upper two quartiles, VIQ correlated higher with academic measures than did VIQ-ELP for both Blacks and Hispanics in almost half of the comparisons. In conclusion, it appears that some subtests of the SOMPA may have some validity for predicting school achievement for students from different ethnic groups.     

Differential genetic etiology of reading disability as a function of IQ

To test the hypothesis that the genetic etiology of reading disability differs as a function of IQ, composite reading performance data from 223 pairs of identical twins and 169 pairs of same-gender fraternal twins in which at least one member of each pair was classified with reading disability were subjected to multiple regression analysis (DeFries & Fulker, 1985, 1988). In the total sample, heritability of the group deficit in reading performance (h(g)2) was .58 (+/- .08). However, when the basic regression model was fitted separately to data from twin pairs with average Wechsler (1974, 1981) full scale IQ scores below 100 or 100 and above, resulting estimates of h(g)2 were .43 and .72, respectively, a significant difference (p < or = .03, one-tailed). The results of fitting extended regression models to reading performance and continuous IQ data provide evidence that the genetic etiology of reading disability differs as a linear function of IQ (p < or = .007, one-tailed). These results suggest that IQ is relevant for the diagnosis of reading disability and that environmental influences may be more salient as a cause of reading difficulties in children with lower IQ scores.