Journal of Abnormal Child Psychology, Vol. 20, No. 1, 1992
A Comparison of Behavioral and Attentional Functioning in Children Diagnosed as Hyperactive or Learning-Disabled Paul M. Robins 1,2
The attentional and behavioral functioning of children diagnosed as hyperactive (ADHD), Naming-disabled (LD), and hyperactive~learning-disabled were compared, using standardized behavior rating scales across raters and settings, and results from a battery of standardized neuropsychological tests. The ADHD and L D groups were "pure" samples with respect to comorbidity. Multiple discriminant-function analyses on the behavioral and neuropsychological data showed that one variate made clear-cut discriminations among and between each of the three groups. The constructs self-regulation, task accuracy~planning~speed, and aggression differentiated the three groups, while sustained attention did not. The results lend strong support to the validity of ADHD as a diagnostic entity apart from LD, and suggest that poor self-regulation and inhibition of behavior may be the hallmark of ADHD.
There is debate whether attention-deficit hyperactivity disorder (ADHD) exists as a coherent diagnostic syndrome (Barkley, 1981; Rutter, 1989). Although ADHD is probably the most well studied of childhood disorders (Barkley, 1981; Ross & Ross, 1982; Weiss & Hechtman, 1979), its diagnostic validity is uncertain. One way to test the validity of a syndrome is Manuscript received in final form June 27, 1991. These findings were reported at the Third Florida Conference on Child Health Psychology, Gainesville, Florida, April, 1991. This research was partially supported by a grant from the Alfred I. duPont institute of the Nemours Foundation. Thanks ate expressed to Mary Ellen White for data collection, Joe Glutting for data analysis, and Wayne Adams for reviewing the manuscript. 1Alfred I. duPont Institute, Wilmington, Delaware 19899. 2Address all correspondence to Paul M. Robins, Alfred I. duPont Institute, P.O. Box 296, Wilmington, Delaware 19899. 65 0091-0627/92/0200-0065506.50/09 1992PlenumPublishingCorporation
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to differentiate it from other recognized childhood disorders. ADHD is often closely associated with learning disabilities (LD), as children with LD are also thought to exhibit underlying dysfunctional attentional and memory processes. Investigation of these clinical groups has been compromised by using subjects displaying more than one disorder. There is a clear and identified need to compare children with pure ADHD, children with pure LD, and children with both ADHD and LD (CantweU & Baker, 1991). A comparison of attentional and behavioral functioning in both ADHD and LD child samples addresses the issue of syndrome definition and the nature of the association between ADHD and LD. Historically, the diagnostic validity of ADHD has been suspect for numerous reasons, including (a) lack of agreement among parents and teachers regarding the presence of core ADHD symptoms using behavioral rating scales (Barkley, 1990a); (b) poor convergent and discriminant validity of measures of attention and impulsivity, thereby calling into question whether these symptoms do, in fact, covary (Lovejoy and Rasmussen, 1990); and (c) inconsistency as to whether sustained attention is or ought to be a primary diagnostic criterion. These issues, among others, have thwarted attempts toward more precise diagnostic refinement. There have been a number of investigations specifically exploring the relationship between LD and ADHD. That there is considerable overlap between the two disorders is generally accepted (CantweU & Baker, 1991). For example, August and Garfinkel (1990) found that 39% of children diagnosed ADHD were found to have a coexisting reading LD. However, the nature of this relationship has not been well defined (Epstein, Shaywitz, Shaywitz, & Woolston, 1991). While some researchers have concluded that ADHD does not represent a unique set of cognitive impairments (e.g., Halperin, Gittleman, Klein, & Rudel, 1984; McGee, Williams, Moffit, & Anderson, 1989), others (Douglas and Benezra, 1990) found that distinct types of cognitive profiles characterized the two groups. There continue to be questions regarding the nature of the relationship between ADHD and LD. Weaknesses of previous research exploring dimensions of attentional functioning in children have included (a) unclear and nonrigorous diagnostic criteria for inclusion into diagnostic groups; (b) use of mixed cases, or subjects displaying more than one disorder, vs. use of "pure" ADHD and LD cases; (c) use of nonstandardized tests; and (d) failure to assess both cognitive and behavioral functioning across settings and across observers. This study compared the attentional and behavioral functioning of children diagnosed as LD and/or ADHD using standardized behavior rating scales, and results from a battery of standardized neuropsychological tests believed to be sensitive to deficits in self-regulation, sustained attention,
Diagnostic Validity of ADHD
67
and flexible problem-solving. Multiple sources and types of diagnostic data were purposefully included, emulating "real-world" decision making conditions. Earlier design weaknesses were addressed by using (a) rigorous diagnostic criteria for inclusion into the ADHD and LD groups; (b) "pure" ADHD and LD samples, in addition to a mixed ADHD/LD group; (e) standardized behavioral rating and cognitive assessment instruments; and (d) a multimethod, multidimensional assessment protocol, that is, assessment across methods, settings, and raters.
METHOD
Subjects The total sample consisted of 68 children (56 boys, 12 girls) presenting for evaluation of learning and/or attentional concerns through Divisions of Developmental Medicine or Pediatric Psychology at a children's hospital in Wilmington, Delaware. Three diagnostic groups were compared: ADHD without significant academic concerns (n = 18), LD without A D H D symptoms (n = 25), and a mixed ADHD/LD group (n = 25). The LD sample was identified through multidisciplinary assessment, including a combination of developmental medical, psychological, and educational evaluations. Diagnostic criteria for the LD sample consisted of the following: (a) aged 6 through 12, inclusive; (b) diagnosis of a learning disability based on the consensual validation of a multidisciplinary team (consisting of a developmental pediatrician, pediatric psychologist, and learning disability specialist), using neurodevelopmental, psychological, and educational evaluations, and consistent with the federal requirements established by P.L. 94-142; (c) full-scale Wechsler IQ greater than 85; (d) no behavioral observations during the evaluations of restlessness, impulsivity, and/or short attention span; (e) no previous diagnosis of ADHD; (f) no history or use of a therapeutic trial of psychostimulant medication; and (g) no known major medical diagnoses (e.g., Tourettes syndrome, cerebral palsy, or head trauma/brain injury). Charts were reviewed of children who were previously diagnosed as LD within the past year. Letters were sent to the parents of children who met all 7 research criteria detailed above. Parents were also telephoned in order to explain the purpose of the study and answer any questions. Of the over 150 charts reviewed, 50 met these research criteria, and 25 parents consented to participate. The majority of the LD sample were language/reading-disabled (75%), although it was a mixed LD sample, including nonverbal learning-disabled participants as well.
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LD without attentional concerns appear to represent a relatively rare event within a referral clinic population (Barkley, 1990; Dykman & Ackerman, 1991). Estimates of the prevalence of ADHD in populations with LD has varied from 41% to 80% (Epstein et al., 1991). In this study, less than 37% of LD children seen for multidisciplinary assessment met research criteria for study inclusion, resulting in a relatively small sample size (n = 25). The ADHD children were identified through assessment in the Attention-Deficit Disorder Hyperactivity Program, a subspeciality clinic of the Division of Pediatric Psychology, Department of Pediatrics. The ADHD program is a diagnostic, treatment, and consultation clinic. Referrals are accepted from the child's primary care physician, in most cases a pediatrician. Referrals represent a broad spectrum Of clinic-referred children with primary attentional concerns. Rigorous ADHD diagnostic criteria (Barkley, 1990b) were utilized. These included, but were not limited to, the following: (a) teacher ratings of inattentiveness, impulsivity, and restlessness 2 or more standard deviations above the mean (98%) on the hyperactivity scale of the 28-item revised Conners Teacher Rating Scale (Goyette, Conners, & Ulrich, 1978); (b) age of onset of symptoms by 6 years as reported by parents; (c) duration of symptoms at least 12 months; (d) eight or more DSM-III-R (American Psychiatric Association, 1986) criteria, using a parent checklist format; and (e) exclusion of gross sensory or motor impairment (determined by the referring pediatrician) or severe emotional disturbance. A developmental interview with the child's primary caretakers by the clinic psychologist prior to the assessment was used to determine age of onset (prior to age 6) and duration (longer than 12 months) criteria. In addition to the above ADHD criteria, ADHD/non-LD children met two additional criteria: (a) school administered standardized group achievement test scores within the average range or higher in language, reading, math, and spelling; and (b) no significant and specific academic weaknesses, as reported in writing by the classroom teacher. Of the 50 children diagnosed as ADHD, 18 children did not in addition demonstrate significant academic concerns and thus met the criteria for inclusion. ADHD without significant learning concerns represents a relatively uncommon event within a referral clinic population. Although the prevalence of LD in children with ADHD ranges from 9% to 11% in epidemiological studies (Epstein et al., 1991), comorbidity is generally much greater in referral populations. Dykman and Ackeman (1991) found over half of their ADHD sample were dyslexic or slow learners. In this study, 36% of ADHD referred children met the research criteria for inclusion, resulting in a relatively small sample size (n = 18).
Diagnostic Validity of ADHD
69
Table I. Sample Characteristics of Criterion Groupsa
Demography Age (months) Criterion group ADHD LD ADHD/LD Total 68 aNote:
Sex
M
SD
M
F
n
95.9 112.6 100.8
15.7 22.4 26.5
17 19 20
1 6 5
18 25 25
ADHD = attention-deficit hyperactivitydisorder; LD = learning-disabled.
The A D H D / L D children were also identified through assessment in a A D H D speciality clinic. A child was considered for assignment to the combined A D H D / L D group when the criteria for A D H D were met, as described above. Furthermore, standardized group achievement test scores and school records were used to help determine the presence of LD. That is, a child was considered as LD if either (a) special education services under an LD certification as determined by state and district guidelines were received; and/or (b) school administered yearly group achievement test scores in reading, spelling, and/or mathematics were greater than 1 standard deviation below current grade placement norms; and (c) the child's teacher reported specific concerns with a child's academic achievement in one or more areas. Table I reports the characteristics of the sample by criterion group. The combined sample was largely male (82%), with a mean age of 103 months. The A D H D sample was slightly younger (M = 96 months), while the LD sample was older (M = 113 months) and included proportionally more females (32% vs. 6%). Cases with any missing data were deleted from subsequent discriminant function analyses. There was no differential loss of subjects by group membership, sex, or age (respectively, Z2 = .03, n.s.; Z2 = .03, n.s.; and t = -.05, n.s.). Procedure
Appointments were made for cognitive assessment on an individual basis; children were seen in the outpatient clinic setting of the hospital. Written consent by the parent and verbal assent by the child were obtained prior to the assessment. The tests were individually administered by a trained examiner in a prescribed order. The examiner was blind to the hypotheses under consideration and group membership of the children. Total examination time was approximately 1 hour for each participant.
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Measures
All children underwent assessment using the following battery of tests: (a) Wechsler Intelligence Scale for Children-Revised (digit span, coding, and mazes subtests) (WISC-R; The Psychological Corporation, 1974), (b) Developmental Test of Visual-Motor Integration (Beery, 1982), (c) Trail Making Test (Reitan, 1985), (d) Matching Familiar Figures Test (MFF; Cairns & Cammock, 1978b), (e) Rey Auditory-Verbal Learning Test (AV; Rey, 1958), and (f) the Delay and Vigilance subtests of the Gordon Diagnostic System (GDS; Gordon, 1986). These (sub)tests were selected in order to specifically assess dimensions of self-regulation, sustained attention, and flexible problem solving, in addition to short term verbal memory and visual-motor integration. Tests were administered in a standardized fashion, following instructions outlined in the manual. Parents completed the Child Behavior Checklist (CBCL; Achenbach & Edelbrock, 1983), and the child's current classroom teacher was asked to complete the ADD-H Comprehensive Teacher's Rating Scale (ACTeRS; UUman, Sleator, & Sprague, 1988). The Developmental Test of Visual-Motor Integration (Beery, 1982) is a sequence of 24 geometric forms copied by the child with pencil on paper. Concurrent and predictive validity studies, reported in the manual, suggested significant positive correlations with measures of handwriting, readiness tests, and mental abilities. The Trail Making Test for Children (Parts A & B) (Reitan, 1985) involves connecting a series of circles. Part A consists of 15 circles; each circle contains a number from 1 to 15. The child is required to connect the circles with a pencil line as quickly as possible, proceeding in a numerical sequence. Part B consists of 15 circles; the circles are numbered 1 through 8 and A through G. The child is required to connect the circles, in sequence, alternating between numbers and letters. The score represents the number of seconds required to finish each part. The test requires immediate recognition of the symbolic significance of numbers and letters, ability to scan the page, flexibility in integrating the numerical and alphabetical series, and completing these requirements under the pressure of time (Reitan, 1985). The Matching Familiar Figures Test (Cairns & Cammock, 1978a; 1978b) is a 20-item version adapted from Kagan's well-known 1965 test. The child must choose from six alternative figures the one that preciously matches the model figure. Two scores are represented; the mean number of errors, and the mean latency to first response (in seconds). Norms are provided for children 7 through 12. Impulsive responders are faster and less accurate than reflective responders (Cairns & Cammock, 1978b).
72.9 6.0 63.5 9.0 69.2 5.3
64.6 7.8
62.8 10.0
61.9 8.1
62.2 6.4
66.1 9.5
65.2 8,8
72.5 8,8
67,5 9.0
74.4 10,7
CBINT CBEXTCBSOCW CBHYP
67.7 8.3
62.2 7.6
74.7 9.4
CBAGG
64.9 6.7
60.9 6.0
68.8 6.8
CBDEL
59.3 5.1
63.8 8.1
60.3 6.7
11.2 3.4
19.8 5.4
11.9 3.2
20.1 4.7
10.9 6.3
22.0 4.5
CBSOM ACTA'FFACTHYP
21.2 5.3
24.3 5.8
20.6 4.8
ACTSS
12.4 5.7
10.0 4.8
17.1 7.5
ACTOPP
aNote: N = 44. Tabled values are r o u n d e d to the nearest tenth. A D H D = attention-deficit hyperactivity disorder; L D = learningdisabled; C B I N T = Child Behavior Checklist (CBCL) internalizing; C B E X T = C B C L externalizing; C B S O C W = C B C L social withdrawal; C B H Y P = C B C L hyperactivity; C B A G G = C B C L aggression; C B D E L = C B C L delinquency; C B S O M = C B C L somatization; A C T A T F = A D D - H Comprehensive T e a c h e r ' s Rating Scale ( A C T e R S ) attention; A C F H Y P = A C T e R S hyperactivity; ACTSS = A C T e R S social skills; A C T O P P = A C T e R S oppositional. C B C L scores are T scores. A C T e R S scores are raw scores.
A D H D (n = 14) M SD LD (n = 13) M SD A D H D / L D (n = 17) M SD
Criterion group
Subtest
Table II. Scores of Criterion G r o u p s on the Behavioral Variables a
1.0 0.62 0.61 0.59 0.51 0.16 0.64 -0.25 -0.31 -0.0 -0.28
1.0 0.35 0.68 0.82 0.41 0.40 -0.52 0.10 -0.09 -0.09 1.0 0.43 0.20 -0.09 0.46 0.05 -0.45 0.11 -0.44 1.0 0.42 0.27 0.41 -0.33 -0.14 0.07 -0.44
CBEXT CBSOCW CBHYP
1.0 0.30 0.37 -0.39 0.02 0.0 -0.08
CBAGG
1.0 0.09 -0.27 0.41 0.0 0.08
CBDEL
1.0 -0.08 -0.35 0.16 -0.41
1.0 -0.32 0.22 -0.12
1.0 -0.12 0.59
CBSOM ACTATI'ACTHYP
1.0 --0.40
ACTSS
1.0
ACTOPP
aNote: N = 44. Tabled values are r o u n d e d to the nearest hundredth. C B I N T = Child Behavior Checklist (CBCL) internalizing; C B E X T = C B C L externalizing; C B S O C W = C B C L social withdrawal; C B H Y P = C B C L hyperactivity; C B A G G = C B C L aggression; C B D E L = C B C L delinquency; C B S O M = C B C L somatization; A C T A T I " = A D D - H C o m p r e h e n s i v e T e a c h e r ' s Rating Scale (ACTeRS) attention; A C T H Y P = A C T e R S hyperactivity; A C T S S = A C T e R S social skills; A C T O P P = A C T e R S oppositional.
CBINT CBEXT CBSOCW CBHYP CBAGG CBDEL CBSOM ACTATI" ACTHYP ACTSS ACTOPP
CBINT
Table IIL Bivariate Correlation Matrix for the Behavioral Variablesa
9.1 2.5
9.0 3.6
11.0 2.5
WlSCCOD
7.5 2.2
8.9 1.6
7.9 2.1
WISCDS
9.1 2.2
11.9 2.9
10.8 2.2
WISCMZ
6.2 2.0
8.8 2.8
7.5 1.6
VMI
27.7 9.3
42.6 6.7
24.6 9.6
TLA
6.9 4.0
17.4 11.1
7.0 3.6
1.7 0.5
1.0 0.7
1.7 0.5
MFF-L MFF-E
26.4 5.3
31.8 9.3
32.5 5.8
REY
0.63 0.2
0.74 0.22
0.60 0.16
ER
33.9 20.2
13.8 15.2
38.3 35.0
TOTCOM
6.5 5.3
1.6 1.3
6.6 8.2
COMVAR
34.9 7.5
36.3 8.6
30.0 9.3
TOTC
W l S C - C O D = Wechsler Intelligence Scale for Children-Revised (WISC-R) coding; WISC-DS = WlSC-R digit span; W I S C - M Z = WISC-R mazes; VMI = Developmental Test of Visual-Motor Integration; T L A = Trail Making Test, Part A; M F F - E = Matching Farniliar Figures Test, m e a n errors; M F F - L = Matching Familiar Figures Test, m e a n latency (seconds); R E Y = Rey Auditory-Verbal Learning Test, total n u m b e r of correct responses; E R = Gordon Diagnostic System (GDS) delay task, efficiency ratio; T O T C O M = GDS vigilance task, total n u m b e r of commission errors; C O M V A R = G D S vigilance task, commission variability; T O T C = GDS vigilance task, total n u m b e r correct responses. W l S C - R values are standard scores with M = 10 and SD = 3. V M I values are standard scores with M = 10 and SD = 3.
aNote: N = 48. Tabled values are rounded to the nearest tenth. A D H D = attention-deficit hyperactivity disorder; L D = learning-disabled;
SD
A D H D / L D (n = 15) M
SD
L D (n = 20) M
SD
M
ADHD (n = 13)
Criterion group
Subtest
Table IV. Scores of Criterion Groups on the Neuropsychological Variables a
O
1.0 -0.07 0.22 0.33 -0.35 0.25 -0.29 0.32 0.12 -0.08 -0.08 0.46
1.0 0.33 0.37 -0.09 0.31 -0.21 0.0 -0.11 -0.09 0.0 0.06 1.0 0.44 -0.09 0.45 -0.41 -0.02 0.11 0.0 0.0 0.0
WISCMZ
1.0 -0.09 0.29 -0.19 -0.34 0.09 0.03 0.11 0.14
VMI
1.0 -0.23 0.41 -0.46 -0.27 0.34 0.09 -0.51
~
1.0 -0.71 0.14 0.05 -0.18 -0.11 0.31
MFF-L
1.0 -0.36 -0.16 0.27 0.11 -0.58
MFF-E
1.0 0.0 -0.06 -0.08 0.34
REY
-0.07 0.07 0.14
1.0
ER
Table V. Bivariate Correlation Matrix for the Neuropsychological Variablesa
WISCDS
1.0 0.47 -0.45
TOTCOM
1.0 -0.32
COMVAR
1.0
TOTC
(WISC-R) coding; WISC-DS = WISC-R digit span; WISC-MZ = WISC-R mazes; VMI = Developmental Test of Visual-Motor Integration; TLA = Trail Making Test, Part A; MFF-E = Matching Familiar Figures Test, mean errors; MFF-L = Matching Familiar Figures Test, mean latency; REY = Rey Auditory-Verbal Learning Test; ER = Gordon Diagnostic System (GDS) delay task, efficiency ratio; TOTCOM = GDS vigilance task, total commission errors; COMVAR = GDS vigilance task, commission variability; TOTC = GDS vigilance task, total number correct responses.
aNote: N = 48. Tabled values are rounded to the nearest hundredth. WISC-COD = Wechsler Intelligence Scale for Children-Revised
WISC-COD WISC-DS WISC-MZ VMI TLA MFF-L MFF-E REY ER TOTCOM COMVAR TOTC
WISCCOD
o
Diagnostic Validity of ADHD
75
The Rey Auditory-Verbal Learning Test (Rey, 1958) involves reading a list of 15 simple words followed by immediate recall, using a free-recall paradigm. Additional presentation/recall trials follow. This task evaluates a child's ability to actively learn a list of minimally related words in a serial learning format. The score used was the total number of words recalled over four presentations. The Gordon Diagnostic System (Gordon, 1986) is a commercially available continuous performance test designed to assess deficits in impulse control and sustained attention in children. The delay task measures the ability to refrain from responding using a self-paced format, while the vigilance task assesses self-control and sustained attention over intermediate periods of time. Norms are provided 4 through 16 years of age. The ACTeRS (Ullman, Sleator, & Sprague, 1988) is a 24-item behavioral rating scale, completed by the classroom teacher. Behavioral items are rated on a 5-point Likert scale. The items fall into four factors that are labeled attention, hyperactivity, social skills, and oppositional. Raw scores are converted into percentile scores based on the child's gender. The Child Behavior Checklist (Achenbach & Edelbrock, 1983) is a 11Sitem behavior rating scale, designed to obtain parents' descriptions of a child's behavior in a standardized format. Reliability and validity issues are well described elsewhere. Both the broad-band internalizing and externalizing factor scales, in addition to the social withdrawal, hyperactivity, aggression, delinquency, and somatization subscales, were utilized in this study.
RESULTS Tables II and III display the score characteristics (M, SD) of the criterion groups and the pooled bivariate correlations, respectively, for the behavioral variables. Tables IV and V display the score characteristics (M, SD) of the criterion groups and the pooled bivariate correlations, respectively, for the neuropsychological variables. Multiple discriminant-function analysis was used to explore differences between the three groups on the behavioral data. Results showed that the groups could be differentiated, with one significant variate emerging (Wilks's lamda = .243, X2 = 50.97, df [22, 10], p < .001). Group centroids in the upper part of Table VI show this variate made clear-cut discriminations among and between each of the three groups. The relative contributions of the 11 d e p e n d e n t variables to the group separation were determined through interpretation of discriminant-function-variable correlations. This pattern of correlations (lower part of Table VI) indicates that the behavioral variables of ACTeRS-hyperactivity, ACTeRS-attention,
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Table VI. Group-Centroid and Discriminant-Function-Variable Correlations: BehavioralVariables~ Discriminant Group centroids functions ADHD LD ADHD/LD Variable correlations ACTeRS hyperactivity ACTeRS attention CBCL extemalizing CBCL aggression
1.062 -1.906 0.583 0.722 -0.721 0.424 0.412
aNote: ADHD = attention-deficit hyperactivity disorder; LD =
learning-disabled; ACTeRS = ADD-H Comprehensive Teacher's Rating Scale; CBCL = Child Behavior Checklist. CBCL-externalizing, and CBCL-aggression best defined this function (all r = .72,-.72, .42, and .41, respectively). Combining information from the group-centroid comparisons, as well as from the discriminant-function-variable correlations, shows that the constructs of self-regulation, classroom functioning (e.g., completing assigned tasks, following directions, working well independently), and aggression diff e r e n t i a t e d the three groups; the A D H D and combined A D H D / L D samples were rated as significantly more impulsive, aggressive, and less productive in the classroom than the LD sample. A classification analysis was used to evaluate the practical utility of the discriminations, that is, the ability of the discriminant function to place participants back into their original groupings. The overall hit rate was 79.5% (ADHD = 71.4%, LD -- 84.6%, and A D H D / L D = 82.4%), thereby adding to the overall validity of results. A second multiple discriminant-function analysis was used to explore differences between the three diagnostic groups on the neuropsychological test data. Trails B was dropped from the analysis due to poor and significantly variable performance of the younger children in the sample. Results showed that the groups could be differentiated (Wilks's lamda = .218, Z2 = 60.23, df [24, 11], p < .001), with one significant variate emerging. Group centroids in the upper part of Table VII show this variate made clear-cut discriminations among and between each of the three groups. The relative contributions of the 12 dependent variables to group separation were determined through interpretation of discriminant-function-variable correlations. This pattern of correlations (lower part of Table VII) indicates that the neuropsychological variables MFF-20 (latency), MFF-20 (errors), visual-motor integration, GDS commission variability, GDS total commis-
Diagnostic Validity of ADHD
77
Table VII. Group-Centroid and Discriminant-Function-Variable
Correlations: NeuropsychologicalVariablesa Group centroids ADHD LD ADHD/LD Variable correlations MFF (latency) MFF (errors) VMI GDS commissionvariability GDS total commissions WlSC-R mazes
Discriminant functions -0.757 1.616 -1.499 0.466 -0.402 0.337 -0.328 -0.317 0.316
aADHD attention-deficit hyperactivitydisorder; LD = learningdisabled; MFF = Matching Familiar Figures Test; VMI = Developmental Test of Visual-Motor Integration; GDS = Gordon Diagnostic System; WlSC-R = Wechsler Intelligence Scale for ChildrenRevised. =
sions, and WISC-R mazes best define this function (all r = .47, -.40, .34, - . 3 3 , - . 3 2 , and .32, respectively). Combining information from the group-centroid comparisons, as well as from discriminant-function-variable correlations, shows that the constructs self-regulation and planning/accuracy/speed differentiate the three groups; the A D H D and combined A D H D / L D samples performed more impulsively, less accurately, and were more variable in terms of self-regulation than the L D sample. A classification analysis was used to evaluate the practical utility of the discriminations, that is, the ability of the discriminant function to place participants back into their original groupings. The overall hit rate was 83.3% ( A D H D = 61.5%, LD = 95.0%, and A D H D / L D = 86.7%), thereby adding to the overall validity of results.
DISCUSSION Children identified as either A D H D , LD, or A D H D / L D differed with respect to their performance on both behavioral and neuropsychological measures sensitive to deficits in self-regulation, general classroom functioning (e.g., working well independently, completing assigned tasks, and following directions), aggression, and task accuracy/planning/speed. In general, those in the A D H D or combined A D H D / L D samples were more impulsive, were less accurate when speed of responding was required, worked less well inde-
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pendently, were more aggressive, and functioned less well in the classroom than those in the LD sample. These results lend strong support to the validity of ADHD as a diagnostic entity apart from LD. The hit rates of 79.5% and 83.3% for the behavioral and neuropsychological variables, respectively, indicated that it was possible to accurately predict criterion group membership. The variable sustained attention, as measured by the number of correct responses on the vigilance test of the Gordon Diagnostic System, was not significantly different among the three groups in an across-age-group comparison. Recent research has suggested that the dimension sustained attention may not be a primary diagnostic criterion. For example, while continuous performance task performance has sometimes been shown to effectively differentiate between hyperactive subjects and normal controls (e.g., Schachar & Logan, 1990; Seidel & Joshko, 1990), it has been less clear whether hyperactive subjects and those exhibiting other developmental-type disorders, such as reading disorders, perform differentially (August & Garfinkel, 1990; Kupietz, 1990). Difficulties with sustained attention may be a nonspecific dimension common to a number of disorders including A D H D , LD, mental retardation, and tic disorders (e.g., Tourettes syndrome). Furthermore, children with ADHD cart sustain their attention as well or nearly as well as normals with sufficient activation (Sergeant & van der Meere, 1989), under conditions of high task stimulation, using novel tasks, and in settings providing high rates of immediate reinforcement or punishment (Barkley, 1990a). Thus, poor regulation and inhibition of behavior may be the hallmark of ADHD (Barkley, 1990a); while sustained attention differentiated between normal and "disordered" children, it alone did not effectively differentiate between two types of overlapping childhood developmental disorders. The ADHD sample displayed poorer performance on tasks requiring accuracy under speeded conditions. That is, they were less accurate (made greater errors) and appeared less planful when speed of responding was stressed. Previous research has indicated that the accuracy of performance, as opposed to speed of performance, distinguished hyperactives from controis (Sergeant & van der Meere, 1989). Maintaining the optimal tradeoff between accuracy and speed within a task may be more difficult for ADHD children than normal controls (Sergeant & van der Meere, 1989). The MFF-20 and WISC-R mazes subtests both required planning and encouraged fast but accurate responding. Of equal interest are subtests or tasks that did not effectively differentiate between the groups. The parent CBCL hyperactivity subscale was only moderately correlated (r = 0.24) with the discriminant function. Likewise, social skill, somatization, social withdrawal, and general internalizing symptomatology were not significantly correlated. The CBCL
Diagnostic Validity of ADHD
79
hyperactivity result is surprising. Examination of subscale group means suggests that members of the LD group, who, by definition were not seen as restless, impulsive, or having difficulties with sustained attention by both teacher and clinician input, nonetheless scored near, but not beyond, the critical range (98th percentile or above) on the parent CBCL. Use of multiple methods of behavioral assessment thus appears to be a prudent practice in order to assure diagnostic accuracy and avoid premature diagnosis of A D H D in children with learning disabilities. Likewise, verbal learning over trials (Rey AV) and short-term auditory memory for digits (WlSC-R digit span) did not significantly differ between groups. The issue of memory functions in children with ADHD has only been recently investigated. Preliminary evidence has suggested that children with ADHD, as compared with normal controls, exhibited a distinct memory profile, involving deficits in short-term, one-trial rote verbal and visual memory, while not exhibiting poorer learning over repeated trials. Attentional deficits appeared most noticeable with rote information processing, and were attenuated with increased semantic content (Adams, Robins, and Sheslow, 1991). Performance has also been noted to be poorer on memory tasks requiring "executive" processes such as deliberate rehearsal strategies and careful consideration of response alternatives (Douglas & Benezra, 1990). In addition, issues of comorbidity were addressed. One, the combined effects of ADHD and LD were greater than either alone on many variables, but particularly for visual-motor integration and planning. Deficits in visual-motor integration are frequently noted in children displaying a variety of disorders and are related to the notion of "output failure" (Levine, Oberklaid, & Meltzer, 1981). Two, children in the ADHD sample were rated as exhibiting greater behavioral concerns than the LD sample (e.g., more aggressive, less compliant, and more oppositional). This is not surprising, given the behavioral concerns frequently noted in children with self-regulation deficits (Epstein et al., 1991). Children were not excluded from the ADHD criterion groups in this study based on behavioral difficulties. There is increasing evidence that, although ADHD and conduct disorders frequently co-occur, they represent overlapping but distinct disorders (Barkley, 1991; Epstein et al., 1991). Finally, the criterion groups did not significantly differ with respect to "internalizing" symptomatology, in addition to social skills functioning. Results from the behavioral rating variables thus lend support to the conclusion that the primary hallmarks of ADHD and LD involve self-regulatory or academic issues, respectively, r a t h e r than possible comorbid features such as depression, social withdrawal, and poor social skills. Differential diagnoses of ADHD from other childhood disorders
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using behavioral rating scales, across raters and settings, appear to be a methodologically sound practice. The hit rate of 79.5% obtained in this study suggests that when parent ratings along broad dimensions of externalizing symptomatology, and teacher ratings of a child in the classroom along dimensions of classroom functioning (e.g., independent work, following directions, and persisting with tasks) and hyperactivity (e.g., overactivity, impulsivity, and overreactivity) are combined through clinical decision making, highly accurate diagnostic differentiations can be made between two common and often overlapping developmental disorders. Use of behavioral ratings perhaps is more "ecologically valid" than laboratory tests (Barkley, 1991) and is economically feasible. Weaknesses of the present study included relatively small sample sizes, t h e r e b y affecting not only statistical power, but also the generalizability and possibly replicability of the results. In addition, the diagnostic criteria for the ADHD/LD group were not rigorous for LD determination, as intellectual (IQ) and academic functioning were not assessed on a one-to-one basis. Rather, certification as LD by the State Department of Public Instruction and/or determination of a significant academic weakness through examination of standardized group achievement test scores were used. Related to sample size, no differentiation between LD subtypes was made. While use of a mixed LD sample added to the overall validity of the results, as clear differentiations were nonetheless evident even when using a heterogeneous group of children with learning problems and children with ADHD, distinctions between LD subtypes were not possible. It is thus not clear whether children with language and/or visual-perceptual-based LD significantly differ with respect to their behavioral and attentional functioning. Finally, there is controversy regarding the nature of the overlap between ADHD and conduct disorders, for example, whether conduct disorders exist without symptoms characteristic of ADHD. The present study did not exclude children with behavior difficulties from the ADHD sample. Future research investigating the relationship between memory and attentional functioning in children is indicated. Concerns regarding shortterm memory are often voiced by teachers and parents of children with ADHD. However, concerns regarding auditory processing in general and verbal memory in particular are also often raised in regard to children with reading and learning disabilities. More precise clarification of the association between attention and memory deficits in the two populations and the nature of this relationship requires further investigation and definition. It might also be fruitful to examine the relationship between attentional functioning in subtypes of ADHD and LD. For example, do children with verbal- as opposed to nonverbal-type LD, with and without ADHD, differ
Diagnostic Validity of ADHD
81
with respect to their behavior and attentional profiles? Finally, this research p a r a d i g m might also b e helpful in further examining the behavioral and attentional functioning in children diagnosed with c o n d u c t disorders and A D H D . C a r e f u l a t t e n t i o n to d i a g n o s t i c criteria a n d i d e n t i f y i n g p u r e samples will further address questions related to the diagnostic validity o f A D H D and the nature o f the relationship between A D H D , L D , and conduct disorders.
REFERENCES Achenbach, T. M., & Edelbrock, C. (1983). Manual for the Child Behavior Checklist and Revised Child Behavior Profile. Burlington: University of Vermont. Adams, W., Robins, P., & Sheslow, D. (1991, April). Memory abilities in children with attention deficit hyperactivity disorder. Paper presented at the Third Florida Conference on Child Health Psychology, Gainesville. American Psychiatric Association. (1986). Diagnostic and statistical manual of mental disorders (3rd ed., rex,.). New York: Author. August, G. J., & Garfinkeh B. D. (1990). Comorbidity of ADHD and reading disability among clinic-referred children. Journal of Abnormal ChiM Psychology, 18, 29-45. Barkley, R. (1981). Hyperactive children: A handbook for diagnosis and treatment. New York: Guilford Press. Barkley, R. (1990a). A critique of current diagnostic criteria for attention deficit hyperactivity disorder: Clinical and research implications. Developmental and Behavioral Pediatrics, 11, 343-352. Barkley, R. (1990b). Attention deficit hyperactivi(y disorder: A handbook for diagnosis and treatment. New York: Guilford Press. Barkley, R. (1991). The ecological validity of laboratory and analogue assessment methods of ADHD symptoms. Journal of Abnormal Child Psychology, 19, 149-178. Cairns, E., & Cammock, T. (1978a). Development of a more reliable version of the matching familiar figures test. Developmental Psychology, 5, 555-560. Cairns, E., & Cammock, T. (1978b). The 20-item Matching Familiar Figures Test: Technical data. Unpublished manuscript. Available from authors, University of Ulster at Coleraine. CantweU, D. P., & Baker, L. (1991). Association between attention deficit-hyperactivity disorder and learning disorders. Journal of Learning Disabilities, 24, 88-95. Douglas, V. I., & Benezra, E. (1990). Supraspan verbal memory in attention deficit disorder with hyperactivity normal and reading-disabled boys. Journal of Abnormal Child Psychology, 18, 617-638. Dykman, R. A., & Ackerman, P. T. (1991). Attention deficit disorder and specific reading disability: Separate but often overlapping disorders. Journal of Learning Disabilities, 24, 96-103. Epstein, M. A., Shaywitz, S. E., Shaywitz, B. A., & Woolston, J. L (1991). The boundaries of attention deficit disorder. Journal of Learning Disabilities, 24, 78-86. Gordon, M. (1986). The Gordon Diagnostic SysterrL DeWitt, NY: Gordon Systems. Gioyette, C. H., Conners, C. K., & Ultrich, R. F. (1978). Normative data on Revised Conners parent and Teacher Rating Scales. Journal of Abnormal Child Psychology, 6, 221-226. Halperin, J., Gittelman, R., Klein, D., & Rudel, R. (1984). Reading disabled hyperactive children: A distinct subgroup of attention deficit disorder with hyperactivity? Journal of Abnormal Child Psychology, 12, 1-14. Kupietz, S. (1990). Sustained attention in normal and in reading-disabled youngsters with and without ADHD. Journal of Abnormal Child Psychology, 18, 357-372.
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Levine, M. D., Oberklaid, F., & Meltzer, L (1981). Developmental output failure: A study of low productivity in school-aged children. Pediatrics, 67, 18-25. Lovejoy, M. C., & Rasmussen, N. H. (1990). The validity of vigilance tasks in differential diagnosis of children referred for attention and learning problems. Journal of Abnormal Child Psychology, 18, 671-681. McGee, R., Williams, S., Moffitt, T., & Anderson, J. (1989). A comparison of 13-year-old boys with attention deficit and/or reading disorder on neuropsychological measures. Journal of Abnormal Child Psychology, 17, 37-53. Psychological Corporation (1974). Wechsler Intelligence Scale for Children-Revised. New York: Author. Reitan, R. (1985). The Halstead-Reitan Neuropsychological Test Battery: Theory and clinical interpretatiorL Tucson, AZ: Neuropsychology Press. Rey, A. (1958). L'E~,amen Clinique en Psychologie. Paris: Presses Universitaires de France. Ross, D. M., & Ross, S. A. (1982). Hyperactivity: Current issues, research, and theory (2nd ed.). New York: Wiley. Rutter, M. (1989). Attention deficit disorder/hyperkinetic syndrome: Conceptual and research issues regarding diagnosis and classification. In T. Sagvolden & T. Archer (Eds.),Attention deficit disorder: clinical and basic research (pp. 1-24). Hillsdale, NJ: Erlbaum. Schachar, R., & Logan, G. (1990). Are hyperactive children deficient in attentional capacity? Journal of Abnormal Child Psychology, 18, 493-513. Seidel, W., & Joschko, M. (1990). Evidence of difficulties in sustained attention in children with ADHD. Journal of Abnormal Child Psychology, 18, 217-229. Sergeant, J., & van der Meere, J. (1989). The diagnostic significance of attentional processing: Its significance for ADDH classification - A future DSM. In T. Sagnolden & T. Archer (Eds.), Attention deficit disorder: Clinical and basic research (pp. 151-166). Hillsdale, NJ: Erlbaum. Ullmann, R. K., Sieator, E. IC, & Sprague, R. L. (1988). Manual for the ADD-H Comprehensive Teacher's Rating Scale. Champaign, ILL: Metri Tech. Weiss, G., & Hechtman, L. (1979). The hyperactive child syndrome. Science, 205, 1348-1354.
A Comparison of Behavioral and Attentional Functioning in Children Diagnosed as Hyperactive or Learning-Disabled Paul M. Robins 1,2
The attentional and behavioral functioning of children diagnosed as hyperactive (ADHD), Naming-disabled (LD), and hyperactive~learning-disabled were compared, using standardized behavior rating scales across raters and settings, and results from a battery of standardized neuropsychological tests. The ADHD and L D groups were "pure" samples with respect to comorbidity. Multiple discriminant-function analyses on the behavioral and neuropsychological data showed that one variate made clear-cut discriminations among and between each of the three groups. The constructs self-regulation, task accuracy~planning~speed, and aggression differentiated the three groups, while sustained attention did not. The results lend strong support to the validity of ADHD as a diagnostic entity apart from LD, and suggest that poor self-regulation and inhibition of behavior may be the hallmark of ADHD.
There is debate whether attention-deficit hyperactivity disorder (ADHD) exists as a coherent diagnostic syndrome (Barkley, 1981; Rutter, 1989). Although ADHD is probably the most well studied of childhood disorders (Barkley, 1981; Ross & Ross, 1982; Weiss & Hechtman, 1979), its diagnostic validity is uncertain. One way to test the validity of a syndrome is Manuscript received in final form June 27, 1991. These findings were reported at the Third Florida Conference on Child Health Psychology, Gainesville, Florida, April, 1991. This research was partially supported by a grant from the Alfred I. duPont institute of the Nemours Foundation. Thanks ate expressed to Mary Ellen White for data collection, Joe Glutting for data analysis, and Wayne Adams for reviewing the manuscript. 1Alfred I. duPont Institute, Wilmington, Delaware 19899. 2Address all correspondence to Paul M. Robins, Alfred I. duPont Institute, P.O. Box 296, Wilmington, Delaware 19899. 65 0091-0627/92/0200-0065506.50/09 1992PlenumPublishingCorporation
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to differentiate it from other recognized childhood disorders. ADHD is often closely associated with learning disabilities (LD), as children with LD are also thought to exhibit underlying dysfunctional attentional and memory processes. Investigation of these clinical groups has been compromised by using subjects displaying more than one disorder. There is a clear and identified need to compare children with pure ADHD, children with pure LD, and children with both ADHD and LD (CantweU & Baker, 1991). A comparison of attentional and behavioral functioning in both ADHD and LD child samples addresses the issue of syndrome definition and the nature of the association between ADHD and LD. Historically, the diagnostic validity of ADHD has been suspect for numerous reasons, including (a) lack of agreement among parents and teachers regarding the presence of core ADHD symptoms using behavioral rating scales (Barkley, 1990a); (b) poor convergent and discriminant validity of measures of attention and impulsivity, thereby calling into question whether these symptoms do, in fact, covary (Lovejoy and Rasmussen, 1990); and (c) inconsistency as to whether sustained attention is or ought to be a primary diagnostic criterion. These issues, among others, have thwarted attempts toward more precise diagnostic refinement. There have been a number of investigations specifically exploring the relationship between LD and ADHD. That there is considerable overlap between the two disorders is generally accepted (CantweU & Baker, 1991). For example, August and Garfinkel (1990) found that 39% of children diagnosed ADHD were found to have a coexisting reading LD. However, the nature of this relationship has not been well defined (Epstein, Shaywitz, Shaywitz, & Woolston, 1991). While some researchers have concluded that ADHD does not represent a unique set of cognitive impairments (e.g., Halperin, Gittleman, Klein, & Rudel, 1984; McGee, Williams, Moffit, & Anderson, 1989), others (Douglas and Benezra, 1990) found that distinct types of cognitive profiles characterized the two groups. There continue to be questions regarding the nature of the relationship between ADHD and LD. Weaknesses of previous research exploring dimensions of attentional functioning in children have included (a) unclear and nonrigorous diagnostic criteria for inclusion into diagnostic groups; (b) use of mixed cases, or subjects displaying more than one disorder, vs. use of "pure" ADHD and LD cases; (c) use of nonstandardized tests; and (d) failure to assess both cognitive and behavioral functioning across settings and across observers. This study compared the attentional and behavioral functioning of children diagnosed as LD and/or ADHD using standardized behavior rating scales, and results from a battery of standardized neuropsychological tests believed to be sensitive to deficits in self-regulation, sustained attention,
Diagnostic Validity of ADHD
67
and flexible problem-solving. Multiple sources and types of diagnostic data were purposefully included, emulating "real-world" decision making conditions. Earlier design weaknesses were addressed by using (a) rigorous diagnostic criteria for inclusion into the ADHD and LD groups; (b) "pure" ADHD and LD samples, in addition to a mixed ADHD/LD group; (e) standardized behavioral rating and cognitive assessment instruments; and (d) a multimethod, multidimensional assessment protocol, that is, assessment across methods, settings, and raters.
METHOD
Subjects The total sample consisted of 68 children (56 boys, 12 girls) presenting for evaluation of learning and/or attentional concerns through Divisions of Developmental Medicine or Pediatric Psychology at a children's hospital in Wilmington, Delaware. Three diagnostic groups were compared: ADHD without significant academic concerns (n = 18), LD without A D H D symptoms (n = 25), and a mixed ADHD/LD group (n = 25). The LD sample was identified through multidisciplinary assessment, including a combination of developmental medical, psychological, and educational evaluations. Diagnostic criteria for the LD sample consisted of the following: (a) aged 6 through 12, inclusive; (b) diagnosis of a learning disability based on the consensual validation of a multidisciplinary team (consisting of a developmental pediatrician, pediatric psychologist, and learning disability specialist), using neurodevelopmental, psychological, and educational evaluations, and consistent with the federal requirements established by P.L. 94-142; (c) full-scale Wechsler IQ greater than 85; (d) no behavioral observations during the evaluations of restlessness, impulsivity, and/or short attention span; (e) no previous diagnosis of ADHD; (f) no history or use of a therapeutic trial of psychostimulant medication; and (g) no known major medical diagnoses (e.g., Tourettes syndrome, cerebral palsy, or head trauma/brain injury). Charts were reviewed of children who were previously diagnosed as LD within the past year. Letters were sent to the parents of children who met all 7 research criteria detailed above. Parents were also telephoned in order to explain the purpose of the study and answer any questions. Of the over 150 charts reviewed, 50 met these research criteria, and 25 parents consented to participate. The majority of the LD sample were language/reading-disabled (75%), although it was a mixed LD sample, including nonverbal learning-disabled participants as well.
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LD without attentional concerns appear to represent a relatively rare event within a referral clinic population (Barkley, 1990; Dykman & Ackerman, 1991). Estimates of the prevalence of ADHD in populations with LD has varied from 41% to 80% (Epstein et al., 1991). In this study, less than 37% of LD children seen for multidisciplinary assessment met research criteria for study inclusion, resulting in a relatively small sample size (n = 25). The ADHD children were identified through assessment in the Attention-Deficit Disorder Hyperactivity Program, a subspeciality clinic of the Division of Pediatric Psychology, Department of Pediatrics. The ADHD program is a diagnostic, treatment, and consultation clinic. Referrals are accepted from the child's primary care physician, in most cases a pediatrician. Referrals represent a broad spectrum Of clinic-referred children with primary attentional concerns. Rigorous ADHD diagnostic criteria (Barkley, 1990b) were utilized. These included, but were not limited to, the following: (a) teacher ratings of inattentiveness, impulsivity, and restlessness 2 or more standard deviations above the mean (98%) on the hyperactivity scale of the 28-item revised Conners Teacher Rating Scale (Goyette, Conners, & Ulrich, 1978); (b) age of onset of symptoms by 6 years as reported by parents; (c) duration of symptoms at least 12 months; (d) eight or more DSM-III-R (American Psychiatric Association, 1986) criteria, using a parent checklist format; and (e) exclusion of gross sensory or motor impairment (determined by the referring pediatrician) or severe emotional disturbance. A developmental interview with the child's primary caretakers by the clinic psychologist prior to the assessment was used to determine age of onset (prior to age 6) and duration (longer than 12 months) criteria. In addition to the above ADHD criteria, ADHD/non-LD children met two additional criteria: (a) school administered standardized group achievement test scores within the average range or higher in language, reading, math, and spelling; and (b) no significant and specific academic weaknesses, as reported in writing by the classroom teacher. Of the 50 children diagnosed as ADHD, 18 children did not in addition demonstrate significant academic concerns and thus met the criteria for inclusion. ADHD without significant learning concerns represents a relatively uncommon event within a referral clinic population. Although the prevalence of LD in children with ADHD ranges from 9% to 11% in epidemiological studies (Epstein et al., 1991), comorbidity is generally much greater in referral populations. Dykman and Ackeman (1991) found over half of their ADHD sample were dyslexic or slow learners. In this study, 36% of ADHD referred children met the research criteria for inclusion, resulting in a relatively small sample size (n = 18).
Diagnostic Validity of ADHD
69
Table I. Sample Characteristics of Criterion Groupsa
Demography Age (months) Criterion group ADHD LD ADHD/LD Total 68 aNote:
Sex
M
SD
M
F
n
95.9 112.6 100.8
15.7 22.4 26.5
17 19 20
1 6 5
18 25 25
ADHD = attention-deficit hyperactivitydisorder; LD = learning-disabled.
The A D H D / L D children were also identified through assessment in a A D H D speciality clinic. A child was considered for assignment to the combined A D H D / L D group when the criteria for A D H D were met, as described above. Furthermore, standardized group achievement test scores and school records were used to help determine the presence of LD. That is, a child was considered as LD if either (a) special education services under an LD certification as determined by state and district guidelines were received; and/or (b) school administered yearly group achievement test scores in reading, spelling, and/or mathematics were greater than 1 standard deviation below current grade placement norms; and (c) the child's teacher reported specific concerns with a child's academic achievement in one or more areas. Table I reports the characteristics of the sample by criterion group. The combined sample was largely male (82%), with a mean age of 103 months. The A D H D sample was slightly younger (M = 96 months), while the LD sample was older (M = 113 months) and included proportionally more females (32% vs. 6%). Cases with any missing data were deleted from subsequent discriminant function analyses. There was no differential loss of subjects by group membership, sex, or age (respectively, Z2 = .03, n.s.; Z2 = .03, n.s.; and t = -.05, n.s.). Procedure
Appointments were made for cognitive assessment on an individual basis; children were seen in the outpatient clinic setting of the hospital. Written consent by the parent and verbal assent by the child were obtained prior to the assessment. The tests were individually administered by a trained examiner in a prescribed order. The examiner was blind to the hypotheses under consideration and group membership of the children. Total examination time was approximately 1 hour for each participant.
70
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Measures
All children underwent assessment using the following battery of tests: (a) Wechsler Intelligence Scale for Children-Revised (digit span, coding, and mazes subtests) (WISC-R; The Psychological Corporation, 1974), (b) Developmental Test of Visual-Motor Integration (Beery, 1982), (c) Trail Making Test (Reitan, 1985), (d) Matching Familiar Figures Test (MFF; Cairns & Cammock, 1978b), (e) Rey Auditory-Verbal Learning Test (AV; Rey, 1958), and (f) the Delay and Vigilance subtests of the Gordon Diagnostic System (GDS; Gordon, 1986). These (sub)tests were selected in order to specifically assess dimensions of self-regulation, sustained attention, and flexible problem solving, in addition to short term verbal memory and visual-motor integration. Tests were administered in a standardized fashion, following instructions outlined in the manual. Parents completed the Child Behavior Checklist (CBCL; Achenbach & Edelbrock, 1983), and the child's current classroom teacher was asked to complete the ADD-H Comprehensive Teacher's Rating Scale (ACTeRS; UUman, Sleator, & Sprague, 1988). The Developmental Test of Visual-Motor Integration (Beery, 1982) is a sequence of 24 geometric forms copied by the child with pencil on paper. Concurrent and predictive validity studies, reported in the manual, suggested significant positive correlations with measures of handwriting, readiness tests, and mental abilities. The Trail Making Test for Children (Parts A & B) (Reitan, 1985) involves connecting a series of circles. Part A consists of 15 circles; each circle contains a number from 1 to 15. The child is required to connect the circles with a pencil line as quickly as possible, proceeding in a numerical sequence. Part B consists of 15 circles; the circles are numbered 1 through 8 and A through G. The child is required to connect the circles, in sequence, alternating between numbers and letters. The score represents the number of seconds required to finish each part. The test requires immediate recognition of the symbolic significance of numbers and letters, ability to scan the page, flexibility in integrating the numerical and alphabetical series, and completing these requirements under the pressure of time (Reitan, 1985). The Matching Familiar Figures Test (Cairns & Cammock, 1978a; 1978b) is a 20-item version adapted from Kagan's well-known 1965 test. The child must choose from six alternative figures the one that preciously matches the model figure. Two scores are represented; the mean number of errors, and the mean latency to first response (in seconds). Norms are provided for children 7 through 12. Impulsive responders are faster and less accurate than reflective responders (Cairns & Cammock, 1978b).
72.9 6.0 63.5 9.0 69.2 5.3
64.6 7.8
62.8 10.0
61.9 8.1
62.2 6.4
66.1 9.5
65.2 8,8
72.5 8,8
67,5 9.0
74.4 10,7
CBINT CBEXTCBSOCW CBHYP
67.7 8.3
62.2 7.6
74.7 9.4
CBAGG
64.9 6.7
60.9 6.0
68.8 6.8
CBDEL
59.3 5.1
63.8 8.1
60.3 6.7
11.2 3.4
19.8 5.4
11.9 3.2
20.1 4.7
10.9 6.3
22.0 4.5
CBSOM ACTA'FFACTHYP
21.2 5.3
24.3 5.8
20.6 4.8
ACTSS
12.4 5.7
10.0 4.8
17.1 7.5
ACTOPP
aNote: N = 44. Tabled values are r o u n d e d to the nearest tenth. A D H D = attention-deficit hyperactivity disorder; L D = learningdisabled; C B I N T = Child Behavior Checklist (CBCL) internalizing; C B E X T = C B C L externalizing; C B S O C W = C B C L social withdrawal; C B H Y P = C B C L hyperactivity; C B A G G = C B C L aggression; C B D E L = C B C L delinquency; C B S O M = C B C L somatization; A C T A T F = A D D - H Comprehensive T e a c h e r ' s Rating Scale ( A C T e R S ) attention; A C F H Y P = A C T e R S hyperactivity; ACTSS = A C T e R S social skills; A C T O P P = A C T e R S oppositional. C B C L scores are T scores. A C T e R S scores are raw scores.
A D H D (n = 14) M SD LD (n = 13) M SD A D H D / L D (n = 17) M SD
Criterion group
Subtest
Table II. Scores of Criterion G r o u p s on the Behavioral Variables a
1.0 0.62 0.61 0.59 0.51 0.16 0.64 -0.25 -0.31 -0.0 -0.28
1.0 0.35 0.68 0.82 0.41 0.40 -0.52 0.10 -0.09 -0.09 1.0 0.43 0.20 -0.09 0.46 0.05 -0.45 0.11 -0.44 1.0 0.42 0.27 0.41 -0.33 -0.14 0.07 -0.44
CBEXT CBSOCW CBHYP
1.0 0.30 0.37 -0.39 0.02 0.0 -0.08
CBAGG
1.0 0.09 -0.27 0.41 0.0 0.08
CBDEL
1.0 -0.08 -0.35 0.16 -0.41
1.0 -0.32 0.22 -0.12
1.0 -0.12 0.59
CBSOM ACTATI'ACTHYP
1.0 --0.40
ACTSS
1.0
ACTOPP
aNote: N = 44. Tabled values are r o u n d e d to the nearest hundredth. C B I N T = Child Behavior Checklist (CBCL) internalizing; C B E X T = C B C L externalizing; C B S O C W = C B C L social withdrawal; C B H Y P = C B C L hyperactivity; C B A G G = C B C L aggression; C B D E L = C B C L delinquency; C B S O M = C B C L somatization; A C T A T I " = A D D - H C o m p r e h e n s i v e T e a c h e r ' s Rating Scale (ACTeRS) attention; A C T H Y P = A C T e R S hyperactivity; A C T S S = A C T e R S social skills; A C T O P P = A C T e R S oppositional.
CBINT CBEXT CBSOCW CBHYP CBAGG CBDEL CBSOM ACTATI" ACTHYP ACTSS ACTOPP
CBINT
Table IIL Bivariate Correlation Matrix for the Behavioral Variablesa
9.1 2.5
9.0 3.6
11.0 2.5
WlSCCOD
7.5 2.2
8.9 1.6
7.9 2.1
WISCDS
9.1 2.2
11.9 2.9
10.8 2.2
WISCMZ
6.2 2.0
8.8 2.8
7.5 1.6
VMI
27.7 9.3
42.6 6.7
24.6 9.6
TLA
6.9 4.0
17.4 11.1
7.0 3.6
1.7 0.5
1.0 0.7
1.7 0.5
MFF-L MFF-E
26.4 5.3
31.8 9.3
32.5 5.8
REY
0.63 0.2
0.74 0.22
0.60 0.16
ER
33.9 20.2
13.8 15.2
38.3 35.0
TOTCOM
6.5 5.3
1.6 1.3
6.6 8.2
COMVAR
34.9 7.5
36.3 8.6
30.0 9.3
TOTC
W l S C - C O D = Wechsler Intelligence Scale for Children-Revised (WISC-R) coding; WISC-DS = WlSC-R digit span; W I S C - M Z = WISC-R mazes; VMI = Developmental Test of Visual-Motor Integration; T L A = Trail Making Test, Part A; M F F - E = Matching Farniliar Figures Test, m e a n errors; M F F - L = Matching Familiar Figures Test, m e a n latency (seconds); R E Y = Rey Auditory-Verbal Learning Test, total n u m b e r of correct responses; E R = Gordon Diagnostic System (GDS) delay task, efficiency ratio; T O T C O M = GDS vigilance task, total n u m b e r of commission errors; C O M V A R = G D S vigilance task, commission variability; T O T C = GDS vigilance task, total n u m b e r correct responses. W l S C - R values are standard scores with M = 10 and SD = 3. V M I values are standard scores with M = 10 and SD = 3.
aNote: N = 48. Tabled values are rounded to the nearest tenth. A D H D = attention-deficit hyperactivity disorder; L D = learning-disabled;
SD
A D H D / L D (n = 15) M
SD
L D (n = 20) M
SD
M
ADHD (n = 13)
Criterion group
Subtest
Table IV. Scores of Criterion Groups on the Neuropsychological Variables a
O
1.0 -0.07 0.22 0.33 -0.35 0.25 -0.29 0.32 0.12 -0.08 -0.08 0.46
1.0 0.33 0.37 -0.09 0.31 -0.21 0.0 -0.11 -0.09 0.0 0.06 1.0 0.44 -0.09 0.45 -0.41 -0.02 0.11 0.0 0.0 0.0
WISCMZ
1.0 -0.09 0.29 -0.19 -0.34 0.09 0.03 0.11 0.14
VMI
1.0 -0.23 0.41 -0.46 -0.27 0.34 0.09 -0.51
~
1.0 -0.71 0.14 0.05 -0.18 -0.11 0.31
MFF-L
1.0 -0.36 -0.16 0.27 0.11 -0.58
MFF-E
1.0 0.0 -0.06 -0.08 0.34
REY
-0.07 0.07 0.14
1.0
ER
Table V. Bivariate Correlation Matrix for the Neuropsychological Variablesa
WISCDS
1.0 0.47 -0.45
TOTCOM
1.0 -0.32
COMVAR
1.0
TOTC
(WISC-R) coding; WISC-DS = WISC-R digit span; WISC-MZ = WISC-R mazes; VMI = Developmental Test of Visual-Motor Integration; TLA = Trail Making Test, Part A; MFF-E = Matching Familiar Figures Test, mean errors; MFF-L = Matching Familiar Figures Test, mean latency; REY = Rey Auditory-Verbal Learning Test; ER = Gordon Diagnostic System (GDS) delay task, efficiency ratio; TOTCOM = GDS vigilance task, total commission errors; COMVAR = GDS vigilance task, commission variability; TOTC = GDS vigilance task, total number correct responses.
aNote: N = 48. Tabled values are rounded to the nearest hundredth. WISC-COD = Wechsler Intelligence Scale for Children-Revised
WISC-COD WISC-DS WISC-MZ VMI TLA MFF-L MFF-E REY ER TOTCOM COMVAR TOTC
WISCCOD
o
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The Rey Auditory-Verbal Learning Test (Rey, 1958) involves reading a list of 15 simple words followed by immediate recall, using a free-recall paradigm. Additional presentation/recall trials follow. This task evaluates a child's ability to actively learn a list of minimally related words in a serial learning format. The score used was the total number of words recalled over four presentations. The Gordon Diagnostic System (Gordon, 1986) is a commercially available continuous performance test designed to assess deficits in impulse control and sustained attention in children. The delay task measures the ability to refrain from responding using a self-paced format, while the vigilance task assesses self-control and sustained attention over intermediate periods of time. Norms are provided 4 through 16 years of age. The ACTeRS (Ullman, Sleator, & Sprague, 1988) is a 24-item behavioral rating scale, completed by the classroom teacher. Behavioral items are rated on a 5-point Likert scale. The items fall into four factors that are labeled attention, hyperactivity, social skills, and oppositional. Raw scores are converted into percentile scores based on the child's gender. The Child Behavior Checklist (Achenbach & Edelbrock, 1983) is a 11Sitem behavior rating scale, designed to obtain parents' descriptions of a child's behavior in a standardized format. Reliability and validity issues are well described elsewhere. Both the broad-band internalizing and externalizing factor scales, in addition to the social withdrawal, hyperactivity, aggression, delinquency, and somatization subscales, were utilized in this study.
RESULTS Tables II and III display the score characteristics (M, SD) of the criterion groups and the pooled bivariate correlations, respectively, for the behavioral variables. Tables IV and V display the score characteristics (M, SD) of the criterion groups and the pooled bivariate correlations, respectively, for the neuropsychological variables. Multiple discriminant-function analysis was used to explore differences between the three groups on the behavioral data. Results showed that the groups could be differentiated, with one significant variate emerging (Wilks's lamda = .243, X2 = 50.97, df [22, 10], p < .001). Group centroids in the upper part of Table VI show this variate made clear-cut discriminations among and between each of the three groups. The relative contributions of the 11 d e p e n d e n t variables to the group separation were determined through interpretation of discriminant-function-variable correlations. This pattern of correlations (lower part of Table VI) indicates that the behavioral variables of ACTeRS-hyperactivity, ACTeRS-attention,
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Table VI. Group-Centroid and Discriminant-Function-Variable Correlations: BehavioralVariables~ Discriminant Group centroids functions ADHD LD ADHD/LD Variable correlations ACTeRS hyperactivity ACTeRS attention CBCL extemalizing CBCL aggression
1.062 -1.906 0.583 0.722 -0.721 0.424 0.412
aNote: ADHD = attention-deficit hyperactivity disorder; LD =
learning-disabled; ACTeRS = ADD-H Comprehensive Teacher's Rating Scale; CBCL = Child Behavior Checklist. CBCL-externalizing, and CBCL-aggression best defined this function (all r = .72,-.72, .42, and .41, respectively). Combining information from the group-centroid comparisons, as well as from the discriminant-function-variable correlations, shows that the constructs of self-regulation, classroom functioning (e.g., completing assigned tasks, following directions, working well independently), and aggression diff e r e n t i a t e d the three groups; the A D H D and combined A D H D / L D samples were rated as significantly more impulsive, aggressive, and less productive in the classroom than the LD sample. A classification analysis was used to evaluate the practical utility of the discriminations, that is, the ability of the discriminant function to place participants back into their original groupings. The overall hit rate was 79.5% (ADHD = 71.4%, LD -- 84.6%, and A D H D / L D = 82.4%), thereby adding to the overall validity of results. A second multiple discriminant-function analysis was used to explore differences between the three diagnostic groups on the neuropsychological test data. Trails B was dropped from the analysis due to poor and significantly variable performance of the younger children in the sample. Results showed that the groups could be differentiated (Wilks's lamda = .218, Z2 = 60.23, df [24, 11], p < .001), with one significant variate emerging. Group centroids in the upper part of Table VII show this variate made clear-cut discriminations among and between each of the three groups. The relative contributions of the 12 dependent variables to group separation were determined through interpretation of discriminant-function-variable correlations. This pattern of correlations (lower part of Table VII) indicates that the neuropsychological variables MFF-20 (latency), MFF-20 (errors), visual-motor integration, GDS commission variability, GDS total commis-
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Table VII. Group-Centroid and Discriminant-Function-Variable
Correlations: NeuropsychologicalVariablesa Group centroids ADHD LD ADHD/LD Variable correlations MFF (latency) MFF (errors) VMI GDS commissionvariability GDS total commissions WlSC-R mazes
Discriminant functions -0.757 1.616 -1.499 0.466 -0.402 0.337 -0.328 -0.317 0.316
aADHD attention-deficit hyperactivitydisorder; LD = learningdisabled; MFF = Matching Familiar Figures Test; VMI = Developmental Test of Visual-Motor Integration; GDS = Gordon Diagnostic System; WlSC-R = Wechsler Intelligence Scale for ChildrenRevised. =
sions, and WISC-R mazes best define this function (all r = .47, -.40, .34, - . 3 3 , - . 3 2 , and .32, respectively). Combining information from the group-centroid comparisons, as well as from discriminant-function-variable correlations, shows that the constructs self-regulation and planning/accuracy/speed differentiate the three groups; the A D H D and combined A D H D / L D samples performed more impulsively, less accurately, and were more variable in terms of self-regulation than the L D sample. A classification analysis was used to evaluate the practical utility of the discriminations, that is, the ability of the discriminant function to place participants back into their original groupings. The overall hit rate was 83.3% ( A D H D = 61.5%, LD = 95.0%, and A D H D / L D = 86.7%), thereby adding to the overall validity of results.
DISCUSSION Children identified as either A D H D , LD, or A D H D / L D differed with respect to their performance on both behavioral and neuropsychological measures sensitive to deficits in self-regulation, general classroom functioning (e.g., working well independently, completing assigned tasks, and following directions), aggression, and task accuracy/planning/speed. In general, those in the A D H D or combined A D H D / L D samples were more impulsive, were less accurate when speed of responding was required, worked less well inde-
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pendently, were more aggressive, and functioned less well in the classroom than those in the LD sample. These results lend strong support to the validity of ADHD as a diagnostic entity apart from LD. The hit rates of 79.5% and 83.3% for the behavioral and neuropsychological variables, respectively, indicated that it was possible to accurately predict criterion group membership. The variable sustained attention, as measured by the number of correct responses on the vigilance test of the Gordon Diagnostic System, was not significantly different among the three groups in an across-age-group comparison. Recent research has suggested that the dimension sustained attention may not be a primary diagnostic criterion. For example, while continuous performance task performance has sometimes been shown to effectively differentiate between hyperactive subjects and normal controls (e.g., Schachar & Logan, 1990; Seidel & Joshko, 1990), it has been less clear whether hyperactive subjects and those exhibiting other developmental-type disorders, such as reading disorders, perform differentially (August & Garfinkel, 1990; Kupietz, 1990). Difficulties with sustained attention may be a nonspecific dimension common to a number of disorders including A D H D , LD, mental retardation, and tic disorders (e.g., Tourettes syndrome). Furthermore, children with ADHD cart sustain their attention as well or nearly as well as normals with sufficient activation (Sergeant & van der Meere, 1989), under conditions of high task stimulation, using novel tasks, and in settings providing high rates of immediate reinforcement or punishment (Barkley, 1990a). Thus, poor regulation and inhibition of behavior may be the hallmark of ADHD (Barkley, 1990a); while sustained attention differentiated between normal and "disordered" children, it alone did not effectively differentiate between two types of overlapping childhood developmental disorders. The ADHD sample displayed poorer performance on tasks requiring accuracy under speeded conditions. That is, they were less accurate (made greater errors) and appeared less planful when speed of responding was stressed. Previous research has indicated that the accuracy of performance, as opposed to speed of performance, distinguished hyperactives from controis (Sergeant & van der Meere, 1989). Maintaining the optimal tradeoff between accuracy and speed within a task may be more difficult for ADHD children than normal controls (Sergeant & van der Meere, 1989). The MFF-20 and WISC-R mazes subtests both required planning and encouraged fast but accurate responding. Of equal interest are subtests or tasks that did not effectively differentiate between the groups. The parent CBCL hyperactivity subscale was only moderately correlated (r = 0.24) with the discriminant function. Likewise, social skill, somatization, social withdrawal, and general internalizing symptomatology were not significantly correlated. The CBCL
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hyperactivity result is surprising. Examination of subscale group means suggests that members of the LD group, who, by definition were not seen as restless, impulsive, or having difficulties with sustained attention by both teacher and clinician input, nonetheless scored near, but not beyond, the critical range (98th percentile or above) on the parent CBCL. Use of multiple methods of behavioral assessment thus appears to be a prudent practice in order to assure diagnostic accuracy and avoid premature diagnosis of A D H D in children with learning disabilities. Likewise, verbal learning over trials (Rey AV) and short-term auditory memory for digits (WlSC-R digit span) did not significantly differ between groups. The issue of memory functions in children with ADHD has only been recently investigated. Preliminary evidence has suggested that children with ADHD, as compared with normal controls, exhibited a distinct memory profile, involving deficits in short-term, one-trial rote verbal and visual memory, while not exhibiting poorer learning over repeated trials. Attentional deficits appeared most noticeable with rote information processing, and were attenuated with increased semantic content (Adams, Robins, and Sheslow, 1991). Performance has also been noted to be poorer on memory tasks requiring "executive" processes such as deliberate rehearsal strategies and careful consideration of response alternatives (Douglas & Benezra, 1990). In addition, issues of comorbidity were addressed. One, the combined effects of ADHD and LD were greater than either alone on many variables, but particularly for visual-motor integration and planning. Deficits in visual-motor integration are frequently noted in children displaying a variety of disorders and are related to the notion of "output failure" (Levine, Oberklaid, & Meltzer, 1981). Two, children in the ADHD sample were rated as exhibiting greater behavioral concerns than the LD sample (e.g., more aggressive, less compliant, and more oppositional). This is not surprising, given the behavioral concerns frequently noted in children with self-regulation deficits (Epstein et al., 1991). Children were not excluded from the ADHD criterion groups in this study based on behavioral difficulties. There is increasing evidence that, although ADHD and conduct disorders frequently co-occur, they represent overlapping but distinct disorders (Barkley, 1991; Epstein et al., 1991). Finally, the criterion groups did not significantly differ with respect to "internalizing" symptomatology, in addition to social skills functioning. Results from the behavioral rating variables thus lend support to the conclusion that the primary hallmarks of ADHD and LD involve self-regulatory or academic issues, respectively, r a t h e r than possible comorbid features such as depression, social withdrawal, and poor social skills. Differential diagnoses of ADHD from other childhood disorders
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using behavioral rating scales, across raters and settings, appear to be a methodologically sound practice. The hit rate of 79.5% obtained in this study suggests that when parent ratings along broad dimensions of externalizing symptomatology, and teacher ratings of a child in the classroom along dimensions of classroom functioning (e.g., independent work, following directions, and persisting with tasks) and hyperactivity (e.g., overactivity, impulsivity, and overreactivity) are combined through clinical decision making, highly accurate diagnostic differentiations can be made between two common and often overlapping developmental disorders. Use of behavioral ratings perhaps is more "ecologically valid" than laboratory tests (Barkley, 1991) and is economically feasible. Weaknesses of the present study included relatively small sample sizes, t h e r e b y affecting not only statistical power, but also the generalizability and possibly replicability of the results. In addition, the diagnostic criteria for the ADHD/LD group were not rigorous for LD determination, as intellectual (IQ) and academic functioning were not assessed on a one-to-one basis. Rather, certification as LD by the State Department of Public Instruction and/or determination of a significant academic weakness through examination of standardized group achievement test scores were used. Related to sample size, no differentiation between LD subtypes was made. While use of a mixed LD sample added to the overall validity of the results, as clear differentiations were nonetheless evident even when using a heterogeneous group of children with learning problems and children with ADHD, distinctions between LD subtypes were not possible. It is thus not clear whether children with language and/or visual-perceptual-based LD significantly differ with respect to their behavioral and attentional functioning. Finally, there is controversy regarding the nature of the overlap between ADHD and conduct disorders, for example, whether conduct disorders exist without symptoms characteristic of ADHD. The present study did not exclude children with behavior difficulties from the ADHD sample. Future research investigating the relationship between memory and attentional functioning in children is indicated. Concerns regarding shortterm memory are often voiced by teachers and parents of children with ADHD. However, concerns regarding auditory processing in general and verbal memory in particular are also often raised in regard to children with reading and learning disabilities. More precise clarification of the association between attention and memory deficits in the two populations and the nature of this relationship requires further investigation and definition. It might also be fruitful to examine the relationship between attentional functioning in subtypes of ADHD and LD. For example, do children with verbal- as opposed to nonverbal-type LD, with and without ADHD, differ
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with respect to their behavior and attentional profiles? Finally, this research p a r a d i g m might also b e helpful in further examining the behavioral and attentional functioning in children diagnosed with c o n d u c t disorders and A D H D . C a r e f u l a t t e n t i o n to d i a g n o s t i c criteria a n d i d e n t i f y i n g p u r e samples will further address questions related to the diagnostic validity o f A D H D and the nature o f the relationship between A D H D , L D , and conduct disorders.
REFERENCES Achenbach, T. M., & Edelbrock, C. (1983). Manual for the Child Behavior Checklist and Revised Child Behavior Profile. Burlington: University of Vermont. Adams, W., Robins, P., & Sheslow, D. (1991, April). Memory abilities in children with attention deficit hyperactivity disorder. Paper presented at the Third Florida Conference on Child Health Psychology, Gainesville. American Psychiatric Association. (1986). Diagnostic and statistical manual of mental disorders (3rd ed., rex,.). New York: Author. August, G. J., & Garfinkeh B. D. (1990). Comorbidity of ADHD and reading disability among clinic-referred children. Journal of Abnormal ChiM Psychology, 18, 29-45. Barkley, R. (1981). Hyperactive children: A handbook for diagnosis and treatment. New York: Guilford Press. Barkley, R. (1990a). A critique of current diagnostic criteria for attention deficit hyperactivity disorder: Clinical and research implications. Developmental and Behavioral Pediatrics, 11, 343-352. Barkley, R. (1990b). Attention deficit hyperactivi(y disorder: A handbook for diagnosis and treatment. New York: Guilford Press. Barkley, R. (1991). The ecological validity of laboratory and analogue assessment methods of ADHD symptoms. Journal of Abnormal Child Psychology, 19, 149-178. Cairns, E., & Cammock, T. (1978a). Development of a more reliable version of the matching familiar figures test. Developmental Psychology, 5, 555-560. Cairns, E., & Cammock, T. (1978b). The 20-item Matching Familiar Figures Test: Technical data. Unpublished manuscript. Available from authors, University of Ulster at Coleraine. CantweU, D. P., & Baker, L. (1991). Association between attention deficit-hyperactivity disorder and learning disorders. Journal of Learning Disabilities, 24, 88-95. Douglas, V. I., & Benezra, E. (1990). Supraspan verbal memory in attention deficit disorder with hyperactivity normal and reading-disabled boys. Journal of Abnormal Child Psychology, 18, 617-638. Dykman, R. A., & Ackerman, P. T. (1991). Attention deficit disorder and specific reading disability: Separate but often overlapping disorders. Journal of Learning Disabilities, 24, 96-103. Epstein, M. A., Shaywitz, S. E., Shaywitz, B. A., & Woolston, J. L (1991). The boundaries of attention deficit disorder. Journal of Learning Disabilities, 24, 78-86. Gordon, M. (1986). The Gordon Diagnostic SysterrL DeWitt, NY: Gordon Systems. Gioyette, C. H., Conners, C. K., & Ultrich, R. F. (1978). Normative data on Revised Conners parent and Teacher Rating Scales. Journal of Abnormal Child Psychology, 6, 221-226. Halperin, J., Gittelman, R., Klein, D., & Rudel, R. (1984). Reading disabled hyperactive children: A distinct subgroup of attention deficit disorder with hyperactivity? Journal of Abnormal Child Psychology, 12, 1-14. Kupietz, S. (1990). Sustained attention in normal and in reading-disabled youngsters with and without ADHD. Journal of Abnormal Child Psychology, 18, 357-372.
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