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Behavioral subtypes of attention deficit disorder.

* We became concerned with behavioral subtypes of attention deficit disorder (ADD) several years before the recognition of two subtypes in the third volume of the Diagnostic and Statistical Manual of Mental Disorders (DSM) (American Psychiatric Association [APA], 1980). In this article, we provide an historical perspective, through our own work, for the current debate regarding ADD subtypes. We also present a brief overview of studies from other research groups, focusing first on contrasts of children with ADD, with and without hyperactivity, and then on children with ADD, with defiant or aggressive symptoms. Finally, we present arguments for and against subtyping and suggest ways to achieve validation of behavioral subtypes.


From the outset of our research with children with attention problems, we recognized the heterogeneity of this group. In our first large-scale study, we classified boys with ADD into three behavioral groups: hyperactive, normally active, and hypoactive (Dykman & Ackerman, 1976; Dykman, Ackerman, Clements, & Peters, 1971; Dykman, Walls, Suzuki, Ackerman, & Peters, 1970) . The rationale for this subgrouping came from the work of Luria (1961), who studied two groups of children who were seemingly without disabilities, yet performed poorly in the classroom. Drawing on Pavlovian experimentation in central nervous system subtyping, Luria described an excitatory type and an inhibitory type. The excitatory type's characteristics corresponded with those of the hyperactive child, then beginning to claim the interest of American child psychologists and psychiatrists (Wender, 1971; Werry & Quay, 1972). Luria's inhibitory type, characterized by slow execution of purposive movements, had not then engaged research attention; but clinicians knew well such children who, though not disruptive, dawdled and day-dreamed through much of the school day (Clements & Peters, 1962). Their teachers complained that these children didn't carry out instructions well, failed to complete assignments, or inadequately recalled material they read or heard presented. Similar complaints were made of hyperactive children, but the underlying reasons appeared to be different.

When we began our initial study, no appropriate standardized rating scales existed for placing students into behavioral categories. Thus we used the classroom teacher's global rating of activity level (5-point scale, ranging from highly disruptive to well behaved) to classify the boys. Those not rated as disruptive were considered normally active unless the teacher and parents described the child as extremely slow in purposive movements, in which case he was classified as hypoactive. As hypothesized, the hypoactive group was significantly slower on laboratory reaction-time measures than the hyperactive group (Dykman et al., 1970).

Moreover, when we studied these elementary school boys again at age 14 (Ackerman, Dykman, & Peters, 1977), the hyperactive group had accrued numerous reports of episodes of conflict with authority figures (home, school, community), whereas the behavioral reports of the nonhyperactive groups were similar to those for the normal control group. On a self-rating scale (The Minnesota Counseling Inventory), the hyperactive and hypoactive groups had significantly different profiles. The hyperactives had elevated scores on a cluster of traits getting at conflict and control (family relationships, emotional stability, and conformity), whereas the hypoactive teenagers had adverse scores on social relationships, mood, and leadership. The normally active boys had profiles more similar to controls. In the laboratory, the hyperactives showed an inability to conform on the reaction-time key only in response to light signals. Most fiddled with the key during intertrial intervals, which significantly discriminated them from the nonhyperactive subjects. In evaluating family data on this sample, we found one major difference, which was corroborated in a subsequent sample (Ackerman, Elardo, & Dykman, 1979). That is, the hyperactives were typically first or second born to young mothers who had small families. Hypoactives, on the other hand, were later in birth order and had older mothers.

After Conners (1973) developed parent and teacher rating scales appropriate for the identification of children with attention-hyperactivity problems, it became apparent that a sizable portion of children referred for evaluation of the disorder did not meet suggested cutpoints on the hyperactivity factor, but were nonetheless adversely rated on attention items. Thus, we elected to include these nonhyperactive children in our studies, spurred on by earlier findings on hypoactive and normally active groups. Soon thereafter, ADD without hyperactivity (ADD/WO) was recognized as a diagnostic category in DSM-III (APA, 1980).

In the early 1980s, we compared children with ADD/WO and children with ADD with hyperactivity (ADDH) on several measures of cognitive style (Ackerman, Dykman, Holcomb, & McCray, 1982; Ackerman, Dykman, & Oglesby, 1983). We used Kagan's (1964) Matching Familiar Figures Test to assess impulsivity and the Children's Embedded Figures Test (Karp & Konstadt, 1963) to assess field dependence, which can be considered a sort of susceptibility to distraction. We also gave the children the Wechsler Intelligence Scale for Children-Revised (WISC-R), the Wide Range Achievement Test (WRAT), and a reaction-time task that featured high- and low-reward conditions. The instruments and tasks employed showed no clear-cut differences between the ADD/WO and ADDH groups; however, parents and teachers rated the ADDH subjects significantly higher in aggressivity than the ADD/WO children.

Both boys and girls were included in this study, but no conclusive Sex x Group findings emerged. The ADD/WO and ADDH boys also participated in a placebo-drug crossover study of methylphenidate (Ackerman et al., 1982). Teacher ratings showed greater improvement for the ADDH than the ADD/WO group, but on the laboratory tasks the groups improved equivalently on the active drug.

In another sample, ADD/WO and ADDH subjects were contrasted on tasks selected to tap either automatic or effortful information processing (Ackerman, Anhalt, Dykman, & Holcomb, 1986a, 1986b). Again there were no consistent performance differences between the ADD subgroups. Both groups differed significantly from controls on the effortful tasks, for example, those requiring memorization and computation.

In our latest and largest ADD sample (Dykman & Ackerman, 1991), we contrasted three subgroups: ADD/WO, ADDH, and ADDH plus aggression (ADDHA). Although recognition of an ADD/WO subtype was gaining ground, an aggressive subtype had not yet been proposed, this despite the pioneering work of Loney and her colleagues (1987). Loney and associates showed that the much used abbreviated hyperkinesis index (extracted from the Conners [1973] Teacher Questionnaire) actually had two factors: overactive/inattentive and aggressive. Loney's group then found that hyperactive grade-school children with an aggressive overlay had a more adverse outcome in adolescence.

In our recent ADD sample (Dykman & Ackerman, 1991), we used the scores from the two Loney factors and from our ADD index (composed of 10 attention items from DSM-III) to perform a K-means cluster analysis. The rationale and procedures have been published elsewhere (Dykman & Ackerman, 1993). Three clusters were identified: ADD/WO (N = 49), ADDH (N = 63), and ADDHA (N = 47). A disproportionate number of black males were in the ADDHA group, and a disproportionate number of girls were in the ADD/WO group; but there were not enough subjects to allow Sex x Race x Group analyses. Thus, the first report was based on data for the white males only (Dykman & Ackerman, 1991). The three behavioral subgroups were further divided into those who did or did not meet criteria for specific reading disability (RD). Those with RD were equally represented in the three behavioral groups (approximately half of each group).

The three behavioral groups were significantly separated by teacher ratings other than those used to perform the cluster analysis. The major differences were between the ADD/WO and the ADDHA groups. The latter were rated more adversely on socialization skills, impulsivity, and the impatience/aggressive traits associated with the Type A personality (see Matthews & Angulo, 1980, for a description of their rating scale for children). Parents rated the ADDHA group more adversely on the Externalizing Scale of the Child Behavior Checklist (Achenbach & Edelbrock, 1983), but the groups did not differ on the Internalizing Scale. Nor did the groups differ on self-ratings on the Junior Personality Inventory (Eysenck, Eastings, & Eysenck, 1970).

These children with ADD were also administered the Diagnostic Interview for Children and Adolescents (DICA), which is keyed to DSM-III (Herjanic & Reich, 1982). Over half the children had additional self-reported DICA diagnoses, with oppositional disorder and affective (internalizing) disorders most frequent (Livingston, Dykman, & Ackerman, 1990). The ADDHA group had the highest overall rate of DICA diagnoses per child (.94) with ADD/WO next (.90) and ADDH lowest (.75). Significantly more boys with ADDHA had a diagnosis of conduct disorder, but no other differences in rates of specific disorders were found. Within and across the three subgroups, those with and without RD did not differ in rates in any DICA category.

In the laboratory, the subjects were administered three paper-and-pencil performance tasks: a 10-min coding test; a 20-problem timed arithmetic test; and the Trailmaking Test (parts A and B), a part of the Halstead-Reitan battery (Golden, 1981). There were no ADD subgroup differences on any of these tasks or on a computer task developed by Gordon (1979), which purports to measure impulsivity.

The major laboratory procedure used to study the three subgroups was a warned-reaction-time task, which was given under noncontingent and contingent reward conditions. In the noncontingent conditions, the subjects were told they would be given a dollar for doing their best. In the contingent condition, they won 4[cts.] for "fast" responses (computer determined) but lost 2[cts.] for slow responses, and feedback occurred on every trial. The warning stimulus was the word "ready" flashed on the computer screen 5 s prior to the imperative stimuli (tones of three intensity levels). Heart rate (HR) and electroencephalogram (EEG) data were continuously recorded.

In analyzing the HR data, we were interested in ongoing levels as well as beat-to-beat changes to the warning signal and tones (Dykman, Ackerman, & Oglesby, 1992). In the foreperiod following the warning signal, HR typically decelerated steadily up to the point of tone onset. Then there was a rebound acceleration back to, or somewhat above, the prestimulus level. Psychophysiologists generally agree that the deceleration component is associated with anticipatory attention, or readiness, and that the acceleration component is associated with attention focused on response execution (Coles, 1984; Lacey & Lacey, 1974; Porges & Coles, 1982). All ADD subgroups were predicted to show less deceleration in HR than controls because of their hypothesized problem in sustaining readiness to respond.

Significant Sex x Group differences in HR levels and change scores were found. Overall, girls had higher HR levels than boys, and the ADD/WO subjects (both boys and girls) had lower HRs than the other ADD groups. But the boys with ADD/WO had more marked deceleration to the warning signal and greater acceleration to the tones than did the boys with ADDH and ADDHA. Girls with ADD/WO, however, were no more reactive than were girls with ADDH and ADDHA. Girls in the control group had the highest HR levels and were the most reactive to stimuli. Boys in the control group and boys with ADD/WO had similar HR levels and reaction patterns. We concluded that girls with ADD/WO appear to be underaroused, whereas boys with ADD/WO do not. Interestingly, however, the ADD subgroups did not differ in reaction times, although all were significantly slower than controls.

Analyses of the EEG data obtained during the reaction-time tasks revealed the event related potential (ERP) waveform to the warning signal differentiated the ADDHA group from the other two ADD groups and from controls (Newton, Oglesby, Ackerman, & Dykman, under review). The portion of the wave form that was markedly different for the ADDHA group was a negative going slow wave occurring about 800 ms after onset of the word "ready." This slow wave is theorized to index anticipatory attention, and it is greatest in magnitude from the right parietal area (Posner & Petersen, 1990). Interestingly, this slow wave did not discriminate the ADDHA group from the other groups in the noncontingent reward condition, but only in the reward condition. This finding supports the theory of Gray (1975), who has described a Behavioral Inhibitory System and a Behavioral Activation System (withdrawal, approach), which, when out of balance, can lead, respectively, to internalizing and externalizing psychopathology. One hallmark of an overreactive Behavioral Activating (or appetitive motivational) System is a stronger than normal response to reward versus nonreward conditions on laboratory tasks.


There are obviously constraints on generalizing from our studies of four ADD samples. In the earliest of our studies, children were placed in categories on the basis of nonstandardized ratings. In addition, all of our studies have used clinic-referred children, and not all have included girls. Still, even though we have reported as many negative as positive results, we would argue for the recognition in DSM-IV and in the mental health community of three behavioral subtypes of ADD.

In arguing for the recognition of these subtypes, investigators are asked to present data demonstrating convergent and divergent validity. The former challenge, usually tested with rating scales, is far easier than the latter, which is usually tested with performance data and outcome measures. For example, we have consistently used teacher ratings to subtype children with ADD, believing the teacher better able to observe children at attention-demanding work and to compare them to current and past samples of schoolchildren of the same age. If we place children with ADD into subgroups on the basis of one set of teacher ratings and then find that the groups differ significantly on teacher ratings on different scales, this is weak evidence of convergent validity. If the groups differ on parent- or self-ratings, this is stronger evidence of convergent validity. But what we desire most is to find the groups differing on laboratory measures that we have hypothesized to separate the groups, that is, measures that hint at or demonstrate some pathognomonic factors. This type of divergent validity for ADD subtypes has been difficult to demonstrate, perhaps because, as Luria (1961) pointed out, children can perform equally poorly for different reasons. Still, we have used timed tests to little avail; these tests theoretically encourage impulsive responding or attention lapses, which should sort out the ADD/WO and ADDH groups. In reflecting on our earliest investigation, we regret not having continued to seek out and study hypoactive children. These children were significantly slower in reaction-time tasks, and they were not prone to fiddle with the key between trials as were hyperactive children. Moreover, when they were followed up as adolescents, they had different psychological profiles and had experienced few conflicts with authority figures, unlike the hyperactive subjects--very convincing evidence of divergent validity.

In our recent study, in which we contrasted three ADD subgroups for the first time, the best evidence of divergent validity came from the psychophysiological data. The girls with ADD/WO appeared to be underaroused, given their lack of responsivity in HR. Moreover, children with ADDHA gave evidence in their ERP waveforms of an overly reactive appetitive motivation system.


Lahey and Carlson (1991) reviewed the literature on ADD without hyperactivity as diagnosed by DSM-III (APA, 1980) criteria. Lahey and his associates have been at the forefront in arguing for the validity of the ADD/WO category and in criticizing the change to "undifferentiated attention deficit disorder" (UADD) in DSM-III-R (APA, 1987).

Lahey and Carlson (1991) concluded that factor analytic studies consistently identify two largely independent dimensions among the symptoms of ADD: (a) motor hyperactivity and impulsive behavior; and (b) inattention, disorganization, and difficulty in completing tasks. Moreover, when the scores on these two factors are cluster analyzed, two subtypes are identified that essentially correspond to the two subtypes in DSM-III. Lahey and Carlson also presented experimental evidence attesting to both convergent and divergent validity. Convergent validity is provided primarily from various ratings made by parents and teachers; and the evidence is consistent, whether from clinic-referred or school-based samples.

As noted earlier, the critical question is whether these two subtypes differ on other behaviors or characteristics or in terms of etiology, prognosis, or response to treatment. Studies using both school-based and clinic-referred samples have consistently shown children with ADDH to be rated more adversely on impulsivity and aggressive/defiant symptomatology than children with ADD/WO, whereas the latter children are rated more adversely on internalizing symptomatology such as anxiety, depressed mood, and withdrawal or shyness (Barkley, DuPaul, & McMurray, 1990; Berry, Shaywitz, & Shaywitz, 1985; Cantwell & Baker, 1992; Edelbrock, Costello, & Kessler, 1984; Lahey, Schaughency, Strauss, & Frame, 1984; Shaywitz, Shaywitz, Schnell, & Towie, 1988).

Both ADD/WO and ADDH samples exhibit more difficulties in academic areas than controls, but neither group has been consistently found to have greater problems than the other (Carlson, Lahey, & Neeper, 1986; Lahey et al., 1984). Studies contrasting ADD/WO and ADDH groups on cognitive/neuropsychological measures have also provided mixed results. Of those reviewed by Lahey and Carlson (1991), half found few or no group differences. Sargeant and Scholten (1985a, 1985b) studied two small (N = 8) groups of ADD/WO and ADDH children in a visual-search task where speed and accuracy were compared. Compared with controls, both groups were significantly slower; but only the children with ADDH were less accurate. Sargeant and Scholten (1985b) concluded that children with ADDH were less able than those with ADD/WO and control children to meet task demands. That is, the ADDH group's latencies were not consistently related to accuracy, whereas the other groups exhibited the oft-reported speed-accuracy tradeoff. Frank and Ben-Nun (1988) found children with ADDH (N = 21) to show significantly greater abnormalities than children with ADD/WO (N = 11) in visual perception, visual sequential memory, and writing performance. The children with ADDH also showed significantly greater abnormality on "soft" neurological signs.

Barkley, Fischer, Edelbrock, Craig, and Smallish (1990) contrasted larger samples of children with ADDH (N = 42) and ADD/WO (N = 48). In addition to comprehensive ratings obtained from parents and teachers (noted previously), the investigators analyzed performance on the WISC-R and WRAT-R and on several laboratory tasks. They also made behavioral observations as the children performed on selected tasks. The ADDH but not the ADD/WO group had significantly poorer scores than controls on the arithmetic subtest of the WISC-R. The ADD/WO group was significantly poorer on the coding subtest than both the ADDH group and controls. The ADD/WO and ADDH groups did not differ, however, on any of the WRAT-R subtests or in the percentage identified as having specific learning disabilities. On a Continuous Performance Task (CPT), the ADDH group had more errors of omission than the control group; but the two ADD subgroups did not differ. Neither did they differ in errors of commission, even though the mean of the ADDH group was double that of the ADD/WO group (scores were highly variable, however). During the CPT, the children with ADDH were observed to be off-task significantly more than the children with ADD/WO; but during a math problems task, the two subgroups did not differ in ratings of off-task behavior. The ADD/WO group, but not the ADDH group, completed significantly fewer problems than controls. The two groups did not differ in errors or latencies on the Matching Familiar Figures Test, which is hypothesized to measure impulsivity (Kagan, 1964). Nor did the groups differ in activity level as measured by wrist and ankle actometers. Thus, the Barkley, Fischer, et al. (1990) study did not uncover as many performance differences between the ADDH and ADD/WO groups as hypothesized, but the children with ADD/WO were less efficient in coding and solving math problems. As in other studies, parent and teacher ratings and family history measures provided stronger separation of groups.

Barkley et al. (1991) studied approximately half of the children with ADDH and ADD/WO of the previous study (Barkley, Fischer, et al., 1990) in a blinded, placebo-controlled crossover design to assess clinical response to methylphenidate at three dose levels. The groups did not differ significantly on any measures in their response to the medication. However, more children with ADD/WO were clinically judged to have either no clinical response (24%) or as responding best to the low dose (35%), whereas 95% of children with ADDH were judged to be positive responders, and most (71%) were recommended to receive the high dose (15 mg twice a day).


As noted earlier, Loney and her associates at Iowa (1987) first made fellow investigators aware of the importance of an aggressive overlay in children with ADD. But no edition of the DSM has recognized an ADDHA subgroup. Rather, the preference seems to be to assess for co-morbid conditions, and "oppositional defiant disorder" is frequently found. Important to note, Loney's aggression factor, derived from the Abbreviated Hyperkinesis Index (Conners, 1973), includes five items that correspond to DSM-III-R symptoms for oppositional defiant disorder: acts smart (impudent or sassy); temper outbursts; quarrelsome; openly defies authority; and uncooperative with teacher. Thus, it is likely the teacher who rated a child with ADD as aggressive on the Loney factor or some similar scale would also endorse DSM-III-R symptoms of oppositional disorder for the child. None of those items corresponds to symptoms listed for conduct disorder. But oppositional disorder is recognized as a predisposing factor for conduct disorder. Obviously, conduct disorder (which may entail physical aggression, stealing, truancy, etc.) is more apt to be diagnosed in older children than those typically referred for an initial evaluation for ADD.

Shaywitz and Shaywitz (1988) have suggested the recognition of three ADD subtypes: ADD/WO, ADDH, and ADDPlus. Their ADDPlus category presumably would include ADD subjects with any co-morbid diagnosis. Although the ADDPlus category merits considerations, emphasis should probably be placed on aggressive disorders, especially in view of follow-up studies of ADD samples.

Later studies have corroborated the Iowa follow-up studies (Loney, 1987) in showing the importance of aggressive overlay in ADD. For example, Barkley, Fisher, et al. (1990) showed in an 8-year follow-up of hyperactive children that those with oppositional defiant disorder accounted for most of the adverse findings. The presence of the hostile-defiant behavior pattern in adolescence was predicted by the degree of aggression in childhood. Similarly, two follow-up studies of Mannuzza, Gittelman-Klein, and associates point to the presence and risk of aggressive behavior in perhaps a third of hyperactive subjects (Gittelman, Mannuzza, Shenker, & Bonagura, 1985; Mannuzza, Klein, et al. 1991).

August and Stewart (1981) found hyperactive/conduct disordered boys to be more egocentric and behaviorally reactive than nonaggressive hyperactive boys, who had lower verbal IQs and more academic failure. These distinctions were still present at a 4-year follow-up (August, Stewart, & Holmes, 1983). Also, the aggressive group had a higher incidence of antisocial parent pathology (August et al., 1983).

A major follow-up study of more than 900 Swedish youths (Magnusson, 1988) provides further evidence that hyperactive/aggressive behavior in childhood portends adult psychopathy. When these children were 13-years old, their teachers rated them (on a 7-point scale) on aggressiveness, motor restlessness, and lack of concentration. Of 85 boys rated as extremely aggressive at age 13, almost half had been registered for criminal offenses during young adulthood (ages 18 to 26), whereas of the 123 boys rated least aggressive, only 14% were registered, and then only a very small portion for serious crimes. Moreover, when the males were cross-classified on motor restlessness and aggressivity, the combination of the two negative behaviors led to even greater risk for criminality than aggressivity alone. Of the 60 males who were at the extremes on both behaviors, 58% had been registered for an offense, compared with 28% of those who were aggressive only, 38% of those who were restless only, and 16% who were neither aggressive nor restless.

Atkins, Pelham, and Licht (1989) related scores on the two Loney factors (overactive/inattentive and aggressive) to multiple measures of behavior and academic performance in 71 grade school boys. Their findings support separate constructs for hyperactivity and aggression. Strongest evidence for differential validity comes from measures of academic performance, peer ratings, and classroom and playground incidents of disruptive or inappropriate behavior. Pelham, Milich, et al. (1991) found a difference between ADDH boys with and without aggression in their response to staged provocation. High-aggressive subjects were more likely to respond to provocation with aggression than low-aggressive subjects. The provoker was ostensibly another boy in another room who competed with the subject on a reaction-time task. A computer program provided the provocation, which was to take away points from the subject when he responded more slowly than the other boy. The subject could also take away 0-100 points from his competitor. The number of points the subject took away was the measure of aggressivity.

Forness and his associates have conducted studies on "pure" and "mixed" groups of ADDH subjects (Forness, Youpa, Hanna, Cantwell, & Swanson, in press). The mixed-group subjects had a co-morbid diagnosis of oppositional or conduct disorder; the pure-group subjects did not. The two groups were relatively evenly matched on age, IQ, and minority status; but the mixed group was at a statistical disadvantage in two academic areas (math and reading comprehension).

Halperin, O'Brien, et al. (1990) have reported intriguing laboratory performance data separating hyperactive from hyperactive/aggressive subjects. Using a Continuous Performance Task (CPT), Halperin, O'Brien, et al. found that hyperactive subjects had more errors of omission (inattention), whereas hyperactive/aggressive subjects made more errors of commission (impulsivity). Similarly, Aman and Turbott (1986) found that elevated teacher ratings on aggression better predicted errors of commission on a paper-and-pencil cancellation task (also referred to as a "children's checking test"). Halperin, Newcorn, et al. (1990) classified another sample of children with ADD as inattentive or not, based on CPT performance. They found that those who were attentive had more conduct problems, whereas those who were inattentive had greater cognitive deficits.


We lean toward the recognition of three ADD behavioral subtypes: ADD/WO, ADDH, and ADDHA. Within each of these groups, however, further categorization is necessary if we are to pursue a goal of homogeneity. One major division should be learning disabled (LD) or not. Another major division probably should be psychiatric co-morbidity or not, but perhaps only for internalizing disorders. The emphasis on internalizing disorders assumes that most children categorized as ADDHA on the basis of teacher ratings would meet DSM-III-R criteria for oppositional defiant disorder, especially on a consensus diagnosis involving parents, teachers, and clinicians.

Even if researchers could have a large enough sample of children with ADD to achieve adequate numbers in the categories created by the subdivisions we recommend, other factors such as age, IQ, sex, and SES would need to be equalized before the search for divergent (external) validation measures. Given all these constraints, it becomes tempting to give up splitting and become a "lumper," or at least to embrace dimensional rather than categorical analyses. Because correlations among ratings of inattentiveness, overactivity, and aggressivity tend to be moderately high (Hinshaw, 1987), especially if from a common source (e.g., the child's classroom teacher), it may well be that ADD researchers would be better advised to use dimensional analyses. Indeed, several major investigators have voiced strong suspicions about the uniqueness of all childhood diagnostic groups (Rutter, 1988; Werry, Elkind, & Reeves, 1987; Werry, Reeves, & Elkind, 1987).

Still, we believe that more careful splitting may lead to stronger divergent (external) validation of ADD subtypes. The best initial strategy may be to select subjects with more extreme behavioral scores. This approach has been successful for Kagan and his associates (e.g., see Kagan, Reznick, & Snidman, 1988), who have focused on extremely shy young children. These investigators have demonstrated with follow-up data and physiological markers the validity of the categorization. Personality researchers have frequently taken this tack, as, for example, Zuckerman (1983) did in his contrasts of subjects who were high or low in sensation seeking. Our early success in achieving validation for a hypoactive subtype also argues for this strategy.

Having formed such groups, the investigator's next priority should be to select laboratory tasks that will elicit the behavioral traits that differentiate the groups. This step has frustrated most investigators. The Matching Familiar Figures Test (Kagan, 1964), which purports to tap impulsivity, has been disappointing, as has Gordon's (1979) task, which requires the child to wait 6 s between key presses to earn a reward. CPTs have not provided as clear a separation of ADD subtypes as hoped, but Halperin and associates (Halperin, O'Brien, et al., 1990) appear to have improved discrimination by a cross-classification of error type and latency of response.

The concurrent measurement of physiological reactivity during laboratory tasks would seem to be another good strategy in the search for measures that will differentiate ADD subgroups, as is the measurement of neurotransmitter activity. For example, Kagan's group (Kagan et al., 1988) found elevated salivary cortisol levels in their extremely shy (or inhibited) children, and Magnusson's group (1988) found significant negative correlations between teacher ratings of aggressivity and motor restlessness and adrenaline excretion following a math test. The identification of biological markers of ADD subgroups should contribute to the development of better intervention strategies, both behavioral and medicinal. Finally, although follow-up studies are much more demanding than one-time studies, outcome data are probably the most trusted evidence of the validity of a diagnostic group. There is no clear evidence so far as to the long-term outcome of children categorized as ADD/WO, and we all await such a study. The evidence regarding increased risk of psychopathy in boys with ADDHA is convincing, but there has been no specific follow-up of girls with ADD of any subtype.

Even though many issues remain unresolved, educators should be more sensitive to children who, though nondisruptive, have attention disorders. Research indicates they need to be evaluated for both cognitive/achievement and emotional problems. The research of Berry et al. (1985) has suggested that girls with ADD/WO may be a particularly undiagnosed group. Moreover, although hyperactive/aggressive children are more likely to be referred for evaluation and are generally responsive to stimulant medication, it behooves educators to remember that the medication does not cure the disorder. Teachers and counselors, however, should find the medicated defiant/aggressive child more open to suggestions regarding socially acceptable ways to handle irritation and frustration. Aggressive traits, unfortunately, tend to be enduring. Hence, every effort should be made to modify these traits early in the child's life.


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ROSCOE A. DYKMAN, Emeritus Professor of Pediatrics, University of Arkansas for Medical Sciences, and Director of the Psychophysiology Lab, Department of Pediatrics, Arkansas Children's Hospital, Little Rock. PEGGY T. ACKERMAN, Research Associate, Departments of Psychiatry and Pediatrics, University of Arkansas for Medical Sciences, Little Rock.

Preparation of this article was supported in part by Grant #H023S10007 from the Office of Special Education Programs, U. S. Department of Education.

Address correspondence to: Roscoe A. Dykman, Ph.D., Department of Pediatrics, Center for Ambulatory Research and Education, Arkansas Children's Hospital, 800 Marshall Street, Little Rock, AR 72202.
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Author:Dykman, Roscoe A.; Ackerman, Peggy T.
Publication:Exceptional Children
Date:Oct 1, 1993
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