Neuropsychological performance of a sample of ...

Developmental Neuropsychology

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Neuropsychological performance of a sample of adults with ADHD, developmental reading disorder, and controls Lisa L. Weyandt , John A. Rice , Ian Linterman , Linda Mitzlaff & Erik Emert To cite this article: Lisa L. Weyandt , John A. Rice , Ian Linterman , Linda Mitzlaff & Erik Emert (1998) Neuropsychological performance of a sample of adults with ADHD, developmental reading disorder, and controls, Developmental Neuropsychology, 14:4, 643-656, DOI: 10.1080/87565649809540734 To link to this article: http://dx.doi.org/10.1080/87565649809540734

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DEVELOPMENTAL NEUROPSYCHOLOGY, 14(4), 643-656 Copyright © 1998, Lawrence Erlbaum Associates, Inc.

Neuropsychological Performance of a Sample of Adults With ADHD, Developmental Reading Disorder, and Controls Lisa L. Weyandt, John A. Rice, Ian Linterman, Linda Mitzlaff, and Erik Emert Central Washington University Ellensburg, WA

In this study, we investigated the performance of adults with Attention Deficit Hyperactivity Disorder (ADHD), relative to adults with Developmental Reading Disorder (DRD), and controls on a battery of executive function tasks (Wisconsin Card Sorting Test [WCST], Test of Variables of Attention, Tower of Hanoi, and Ravens Progressive Matrices) and several self-report ADHD rating scales (Wender Utah Rating Scale, Patient Behavior Checklist, and the Adult Rating Scale). Sixty-four participants took part in the study (21 with ADHD, 19 with DRD, and 24 controls). Kruskall-Wallis one-way analysis of variance results revealed a significant difference between groups, with the DRD group committing more WCST errors (total and perseveration) than the remaining groups. Group differences were also found on the ADHD ratings scales, with the ADHD group reporting higher ratings. Discriminant Function Analyses (using the rating scales and the neuropsychological tasks) correctly classified 67% and 44% of the cases, respectively. The psychometric properties of the ADHD rating scales were also explored.

Attention Deficit Hyperactivity Disorder (ADHD), characterized by an inability to sustain attention, impulsivity, and hyperactivity is estimated to affect between 3 % to 5% of the school-age population (Barkley, 1990). ADHD was previously believed to be a disorder of childhood, with symptoms attenuating with the onset of puberty (Munoz-Millan & Casteel, 1989). Recent studies (e.g., Barkley, Fischer, Requests for reprints should be sent to Lisa L. Weyandt, Department of Psychology, Central Washington University, 400 East 8th Avenue, Ellensburg, WA 98926-7575. E-mail: [email protected]

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Edelbrok, & Smallish, 1990; Klein & Mannuzza, 1991; Mannuzza, Klein, Bessler, Malloy, & LaPadula, 1993; Mannuzza et al., 1991; Weiss & Hechtman, 1986), however, suggest that the majority of children with ADHD continue to exhibit ADHD symptoms throughout adolescence and adulthood and are often beset with academic and social difficulties. Adolescents with ADHD, for example, have been found to be at greater risk for low academic achievement, grade retention, substance abuse, peer rejection, social skill deficits, and antisocial behavior (Barkley, Fischer, Edelbrock, & Smallish, 1990; Fischer, Barkley, Fletcher, & Smallish, 1993; Weiss, Hechtman, & Perlman, 1978). During young adulthood, studies suggest that individuals with ADHD are frequently involved in theft and pranks, verbal abuse toward others, frequent changes in employment, and many are diagnosed as having Antisocial Personality Disorder (Weiss & Hechtman, 1993). In addition to social and behavioral difficulties, research suggests that children and adolescents with ADHD may have neuropsychological deficits, particularly in the area of executive function. Executive function comprises those abilities that enable individuals to maintain an appropriate problem solving set for attaining future goals. Specifically, according to Reader, Harris, Schuerholz, and Denkla (1994), executive function is a term that refers to a domain of cognitive abilities that includes self-regulation, set maintenance, selective inhibition of responding, and response preparation. A similar definition has been advanced by Becker, Isacc, and Hynd (1987), who viewed executive function as strategic planning, impulse control, organized search, and flexibility of thought and action. Historically, neuropsychology has viewed executive function as frontal lobe activities, and more recently, the prefrontal regions of the brain have been implicated in executive functions (e.g., Luria, 1966; Pennington & Ozonoff, 1994; Castellanos, 1997). As noted by Fletcher (1996), however, the mental operations associated with executive function are complex, and ascribing these operations to the frontal lobes is too general. Recently, Barkley (1997) proposed a unifying theory of ADHD asserting that ADHD comprises deficits in behavioral inhibition with secondary impairments in executive function including (a) working memory, (b) self-regulation, (c) internalized speech, and (d) synthesis of information. Barkley also implicated the frontal lobes in ADHD but similar to Fletcher, acknowledged the complexity of the brain system involved. Various neuropsychological tasks have been used to measure executive function in children, adolescents, and adults, including word fluency, mazes, continuous performance tests, the Stroop Color Word Task (1935), Tower of Hanoi (TOH), Trail Making Test, Wisconsin Card Sorting Test (WCST), and others (e.g., Lezak, 1995; Welsh et al., 1990). The neuropsychological literature is replete with cases of individuals who have sustained brain damage and perform poorly on neuropsychological tasks presumed to measure executive functions. Deficits in executive functions are typically characterized by poor impulse control and planning ability, disorganization, and perseveration. These deficits are analogous to the

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symptoms of ADHD and have led to the hypothesis that ADHD is due to a dysfunction of the frontal lobes (e.g., Lou et al., 1984; Zametkin & Cohen, 1990). Children with ADHD, for example, have been found to perform poorly, relative to children without ADHD, on the WCST, Trail Making Test, Stroop Color Word Test, and Continuous Performance Tests (CPTs; Boucugnani & Jones, 1989; Chelune, Ferguson, Koon, & Dickey, 1986; Rapport, DuPaul, Stoner, & Jones, 1986). Research by Parry (1973);Gorenstein,Mammanto,andSandy(1989);Shue and Douglas (1989); and Reader et al. (1994) also reported differences between children with ADHD and controls on executive function tasks. A number of studies, however, have not found differences between children with and without ADHD on executive tasks. Loge, Statton, and Beatty (1990), for example, compared the performance of children with ADHD and controls on the WCST and on additional neuropsychological measures and found no difference between groups. Similar null results were reported using the Stroop Color Word Task. (Carlson, Lahey, & Neeper 1986; Cohen, Weiss, & Minde, 1972; Fisher, Barkley, Edelbrock, & Smallish (1990). Pennington, Groisser, and Welsh (1993) proposed that the equivocal findings were do to comorbidity of groups and asserted that many children with ADHD have coexisting reading disabilities (RD). The authors advocated for "pure" samples and use of a double dissociation paradigm to eliminate the cognitive processing confound. Results of the Pennington et al. study supported their hypothesis, with "pure ADHD" children performing more poorly on executive function tasks than the RD group. Weyandt and Willis (1994) also used a double dissociation paradigm to investigate the neuropsychological performance of children with "pure" ADHD, relative to children with developmental language disorder, and controls. Their findings indicated that children with ADHD performed more poorly on three executive function tasks (mazes, Matching Familiar Figures Test, and TOH), whereas the developmental language disorder group performed more poorly on the language tasks. Significant group differences were not found, however, on three additional executivefunction tasks (i.e., visual search, verbal fluency, and WCST). More recently, Hall, Halperin, Schwartz, and Newcorn (1997) found significant differences between children with ADHD and those with ADHD plus a reading disability on an executive function CPT measure. Based on their findings, Hall et al. argued that executive function deficits may be primarily present in ADHD children without a reading disability. Collectively, findings from Reader et al. (1994), Weyandt and Willis (1994), and Hall et al. (1997) suggested that specific types of executive function deficits may be characteristic of ADHD and not evident in other clinical populations, although this hypothesis warrants further investigation. A recent area of research concerns executive function in adults with ADHD. As mentioned previously, the majority of children with ADHD continue to display symptoms into adolescence and adulthood; however, a dearth of research exists concerning neuropsychological functioning in adults with ADHD and appropriate

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assessment techniques for this population. Biggs (1995), for example, argued that neuropsychological testing, specifically executive function, is useful in the adult ADHD assessment process; however, she adds that "empirical research on testing adults with ADD is extremely limited" (p. 115). Nevertheless, Biggs and others (e.g., Brown, 1995) recommended that tasks such as the WCST, TOH, Rey-Osterrieth, The Letter Cancellation Task, and the Test of Variable Attention (TOVA) can be useful in the assessment of ADHD in adults. Shaw and Giambra (1993) conducted one of the few studies investigating neuropsychological performance of adults (i.e., college students) with ADHD and found that these participants had more spontaneous intrusive thoughts than control participants while completing a vigilance task. The findings also revealed that the students with ADHD made more errors of commission (i.e., "false alarms") relative to controls. The results were interpreted as supporting hypoarousal and poor inhibitional control models of ADHD. Shaw and Giambra also suggested that adults with ADHD continuously seek optimal levels of sensation, which results in uncontrolled spontaneous thoughts that produce deficits in attentional and inhibitional processes. Buchsbaum et al. (1985), were among the first to explore the prevalence of attention problems in college students, using ameasure of vigilance orsustained attention (the CPT). Four hundred male students participated in the study, and 43 of the participating students were identified by the CPT screening measure as falling in the upper and lower 5% of the scoring distribution. These participants were subsequently administered several neuropsychological tasks (i.e., Stroop test, memory tasks, reaction time, eye movements, visual and auditory evoked potentials). Results revealed between group differences, with the "poor attention CPT group" performing significantly differently than the "good attention CPT group" on evoked potential, reaction time, memory and learning, and Stroop tasks. The groups did not differ on the eye-tracking measure. The poor attention group also reported a higher incidence of hyperactivity than the good attention group, as assessed by a self-report instrument. A limitation of the study involves the inclusion criteria. Specifically, it is unknown whether students with documented ADHD were included in the sample and whether students with documented ADHD would have exhibited deficits in executive functions, relative to individuals without ADHD. Greenberg (1990) developed the TOVA and has reported that the TOVA reliably discriminates control participants and individuals with ADHD. As mentioned previously, the TOVA has been recommended as an assessment tool for adult ADHD, as it purportedly measures inattention and impulsivity. Although information is available concerning TOVA performance of children with ADHD (e.g., Reader et al., 1994), few empirical studies have been conducted concerning TOVA performance of adults. The TOH is also widely used as a measure of executive function, and it requires sequencing, planning, and inhibition of impulsive responding. Similar to the TOVA, a substantial body of research exists concerning

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TOH performance in children; however, information is lacking concerning adult performance. As mentioned previously, the WCST has been used extensively in the ADHD child literature, and findings remain equivocal. Despite the clinical utility of the WCST, little is known about the performance of adults with ADHD on this task. Given the child literature that suggests that executive function deficits often characterize children with ADHD and the recommendation by some researchers and clinicians that executive function tasks be included in adult ADHD assessment, research is warranted in this area. Furthermore, as suggested by Pennington (1993), research that compares the executive function performance of individuals with ADHD relative to a second clinical group is needed to help determine whether executive function deficits exist in the ADHD population and whether these deficits are specific to this clinical group. Research is also needed to explore the psychometric properties of assessment techniques that are currently available for use with the adult population. Therefore, the purposes of this study were to (a) investigate the performance of adults with ADHD relative to a second clinical group (i.e., reading disabled) and a control group on a battery of neuropsychological tasks and to (b) explore the psychometric properties of three self-report ADHD rating scales (Wender Utah Rating Scale [WURS], 1993; Patient Behavior Checklist [PBC], Barkley, 1990; Adult Rating Scale [ARS], Weyandt, 1995). Based on findings from the child and adolescent literature, it was hypothesized that adults with ADHD would perform significantly more poorly on the executive function tasks relative to adults with a reading disability and relative to control participants. Given previous studies that support the discriminant validity of the WURS and ARS (e.g., Ward, Wender, & Reimherr, 1993; Weyandt, Linterman, & Rice, 1995), it was also hypothesized that the self-report rating scales would differentiate adults with ADHD from adults with a DRD and controls.

METHOD Participants Sixty-four participants took part in the study including 21 with ADHD, 19 with Developmental Reading Disorder (DRD), and 24 controls (see Table 1 for additional demographic information). Participants were recruited from a university campus and the surrounding community via newspaper advertisements, posters, and cooperation with the university's Americans with Disabilities Affairs office (ADA). To qualify for the study, participants with ADHD, DRD, or both were required to provide written documentation from a physician or psychologist, verifying either disorder, consistent with criteria from theDiagnostic and Statistical Manual of Mental Disorders (3rd ed., rev. [DSM-HI-R]; American Psychiatric Association, 1987).

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WEYANDT, RICE, LINTERMAN, MITZLAFF, EMERT TABLE 1 Participant Demographic Information Group ADHD

DRD

21

19

24

64

11 10

8 11

7 17

26 38

25.86 9.00

21.53 4.71

23.42 5.08

23.66 6.67

14 4 3

16 3 0

20 3 1

50 10 4

n Sex Men Women

Age M SD Marital status Single Married Divorced

Control

Total

Note. ADHD = Attention Deficit Hyperactivity Disorder; DRD = developmental reading disorder.

Adults with ADHD must have received the diagnosis during childhood and must have been diagnosed as presenting with ADHD symptoms as an adult. The majority (i.e., 62) of the participants were students (2 adults with ADHD were nonstudents). Of the 21 adults with ADHD who participated, 8 were taking medication (2 methylphenidate, 3 dexedrine, 1 prozac, 1 desipramine, 1 imipramine) at the time of the study, all of whom were enrolled as students. Given that the university was in session at the time of the study, students were not asked to cease their medication. Participants were compensated with $ 10 or extra course credit for participation. All participants provided written consent, in accordance with ethical guidelines for research with human participants (American Psychological Association, 1992).

Measures and Procedures The study was completed in a laboratory located on the university's campus. Participants were tested individually (total time was approximately 60 min) and asked to complete four self-report rating scales: ARS (Weyandt et al., 1995), WURS (Ward et al., 1993), PBC (Barkley, 1990), and the Brief Symptom Inventory (BSI; Derogatis, 1992).

ARS. The ARS consists of 25 items derived from DSM-III-R criteria, pertaining to attention, impulsivity, and hyperactivity. The format of the scale is con-

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sistent with ADHD rating scales for children (e.g., The ADHD Rating Scale, DuPaul, 1991), and scoring consists of a 4-point scale. Internal consistency of the ARS as measured by Cronbach's alpha was found to be 0.86, and test-retest reliability at 0.80 (Weyandt et al., 1995). The total score was used as the dependent measure in this study. WURS. The WURS is a 61-item instrument designed to help assess adult's descriptions of their childhood behavior. Ratings between adults with ADHD and controls have been found to differ significantly on the WURS (Ward et al., 1993). The WURS has also been found to correlate moderately with the Parents' Rating Scale (a 10-item modification of the Conners Abbreviated Rating Scale; Ward et al., 1993). The total score was used as the dependent measure in this study. PBC. The PBC is an 18-item instrument designed to help assess ADHD adults (Barkley, 1990). Little information is available concerning the psychometric properties of the PBC. The total score was used as the dependent measure in this study. BSI. The BSI is a 53-item instrument designed to assess overall psychological symptom patterns and has been found to have adequate psychometric properties (Derogatis, 1992). The Global Severity Index of the BSI was used as the dependent measure. After completing the rating scales, participants were administered, in a counterbalanced order, the neuropsychological tasks including a computerized TOH, the TOVA (Greenberg, 1990), the WCST (Grant & Berg, 1948), and the Ravens Standard Progressive Matrices (RSPM; Raven, 1985). TOH. The TOH is a ring transfer task that has been widely used as a measure of executive function (Welsh, Pennington, & Groisser, 1991). The computerized version used in this study is published by the Colorado Neuropsychological Test Company. The dependent measure was number of points achieved. TOVA. The TOVA is a 20-min, visual CPT developed by Greenberg (1990). Normative data exist for ages 4 to 80. The dependent measures of the TOVA included errors of omission and errors of commission and are believed to measure the constructs of inattention and impulsivity. WCST. The WCST (Berg, 1948) has been used as a measure of abstract reasoning and flexibility of thought and action (Lezak, 1995). The dependent measures used in this study included total errors and perseveration errors. A fourth measure, the RSPM (Raven, 1992), was used as a screening task for intelligence.

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RESULTS Means and standard deviations for the executive function tasks are presented in Table 2, whereas means and standard deviations for the rating scales are presented in Table 3. Higher means are associated with greater symptomatology on a given rating scale. To test the first hypothesis that adults with ADHD would perform more poorly on the three neuropsychological tasks, Kruskall-Wallis one-way analyses of variance (K-W ANOVAs) were performed. K-W ANOVA results revealed a significant difference between groups for total errors on the WCST, %2(2, N - 64) = 7.91, p < .05, and perseveration errors on the WCST, x2(2, N=64) = 7.22, p < .05. The multiple comparison procedure for rank means suggested by Dunn (1964) revealed that the rank mean of the DRD group was significantly larger than the rank mean of the conTABLE 2 Rank Means for Executive Function Tasks Between Groups Group Task WCST total errors WCST perseveration errors TOVA commission errors TOVA omission errors TOH total score RSPM

ADHD

DRD

Control

37.17 35.88 34.98 38.00 31.74 29.90

38.00 38.79 34.68 29.79 30.21 29.58

24.06 24.56 28.60 29.83 34.98 37.08

Note. ADHD = Attention Deficit Hyperactivity Disorder; DRD = developmental reading disorder; WCST = Wisconsin Card Sorting Test; TOVA = Test of Variables Attention; TOH=Tower of Hanoi; RSPM = Ravens Standard Progressive Matrices.

TABLE 3 Rank Means for Rating Scales Between Groups Group

Scale

ADHD

DRD

Control

ARS WURS PBC BSI

48.76 40.40 46.38 42.24

28.74 33.09 28.28 28.58

21.25 16.21 22.21 25.48

Note. ADHD = Attention Deficit Hyperactivity Disorder; DRD = Developmental Reading Disorder; ARS = Adult Rating Scale; WURS = Wender Utah Rating Scale; PBC = Patient Behavior Checklist; BSI = Brief Symptom Inventory.

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trol group for WCST total errors, and WCST perseveration errors. Differences were not found between groups on the remaining executive function tasks. Eight adults with ADHD were taking medication (e.g., methylphenidate), and post hoc exploratory analyses were performed to investigate potential medication effects on task performance. No significant differences in neuropsychological task performance were found between adults with ADHD taking and not taking medication on WCST total errors, f(19) = -0.83, p = .42; WCST perseveration errors, t(\9)=-0.74,p = .47; TOVA omission errors, /(19) = .01,p = .99; TOVA commission errors, f(19) = 1.59, p = .13; TOH total score, r(19) = -0.63, p = .54; and RSPM, ?(19) = -0.02, p = .99. Although effort was made to exclude participants with comorbid conditions (i.e., ADHD plus an RD) when recruiting participants, two participants with ADHD reported a history of reading problems after completing the study. Thus, a second post hoc exploratory analysis (K-W ANOVA) was performed after removing from the analyses the data from these participants. Results revealed that the between group differences on the WCST scores remained significant. To test the second hypothesis that participants would perform differently on the rating scales, K-W ANOVAs were computed. Results indicated significant differences on all four scales: ARS, %2(2, N = 64) = 25.56, p < .001; WURS, %2(2, N = 58) = 22.10, p < .001; PBC, X2(2, N=63) = 20.52, p < .001; and the BSI, y}(2, N= 63) = 10.12,p< .01. Using Dunn's (1964) multiple comparison procedure for rank means, results indicated that the rank mean of the ADHD group on the ARS was significantly higher than the rank means of both the DRD and control groups. On the WURS, the rank means of the ADHD and DRD groups were larger than the control group's. On the BPC, the rank mean of the ADHD group was significantly higher than the rank means of both the DRD and control groups. Results of Cronbach's alpha supported the internal consistency of the WURS, ARS, PBC, and BSI as indicated in Table 4. Pearson r correlations between rating scales supported the validity of the ADHD rating scales. Specifically, the ARS was found to correlate more strongly TABLE 4 Internal Consistency of the Rating Scales Scale BSI PBC ARS WURS

Cronbach's Alpha 0.97 0.93 0.94 0.92

Note. BSI = Brief Symptom Inventory; PBC = Patient Behavior Checklist; ARS = Adult Rating Scale; WURS = Wender Utah Rating Scale.

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with the WURS than with the BSI, t(6l) = 2.36, p < .05, and the ARS correlated more strongly with the PBC relative to the BSI, f(61) = 4.28, p < .001. The WURS was also found to correlate more strongly with the ARS than with the BSI, t(6\) = 1.92, p < .05, but the WURS did not correlate more strongly with the PBC than with the BSI. Finally, discriminant function analyses were conducted to explore the ability of rating scales and neuropsycholgical tasks to discriminate groups. Results indicated that, when using the ARS, WURS, and PBC as variables, 66.67% of the cases were correctly classified compared to a 33.33% correct classification by chance, X2(6, JV = 64) = 37.07, p < .001. After removal of the first function, discriminant power was no longer significant, %2(2, N = 64) = 5.79, p = .06. The two discriminant functions accounted for approximately 87% and 13% of the cases, respectively. Of those cases incorrectly classified, 2 were classified as DRD, whereas 4 were classified as controls. Using the scores of the WCST total errors, WCST perseveration errors, TOVA omission, TOVA commission, and the TOH score as dependent variables, results of discriminant function analysis revealed that 43.75% of the cases were correctly classified, compared to a 33.33% correct classification by chance, %2(10, N-= 64) = 11.20, p - .34. The discriminant function accounted for approximately 58% of the variance. Of those cases incorrectly classified, 5 were classified as DRD, and 11 were classified as controls. DISCUSSION The purposes of this study were to investigate the performance of adults with ADHD, adults with DRD, and controls on a battery of executive function tasks, and to explore the psychometric properties of three self-report ADHD rating scales. Results revealed overall group differences on one executive function task, support for the psychometric properties of the adult ADHD rating scales, and discriminant ability of the executive function battery. The first hypothesis, that adults with ADHD would perform more poorly on executive function tasks relative to a second clinical group and a control group, was not supported. Contrary to expectations, results revealed that the performance of ADHD group did not differ significantly from the control group on the WCST, TOH, and TOVA. It is of interest to note, however, that the rank means of the TOVA were highest for the ADHD group on TOVA omission errors, and that the DRD group made significantly more errors on the WCST than the control group. There are several plausible interpretations for these findings, all of which merit further investigation. First, perhaps executive function deficits are characteristic of ADHD but attenuate with age with ADHD. For example, Becker et al. (1987); Passler, Isaac, and Hynd (1985); and Welsh et al. (1990) investigated the executive function performance of nondisabled individuals and found improvement in task

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performance with increasing age. With regard to the ADHD population, Barkley, Grodzinsky, and DuPaul (1992) suggested that age is a confounding variable in the child and adolescent ADHD executive function studies, which may account for the equivocal findings in this body of literature. Specifically, in their review of 22 neuropsychological studies, Barkley et al. reported that adolescents with ADHD tend to make fewer errors than younger children with ADHD. Findings from Moffitt and Silva (1988) and Fischer et al. (1990) support Barkley's interpretation. These findings suggest that this age-related trend may continue into adulthood, although it remains unclear whether ADHD symptomatology decreases or whether the tasks used in this study are insensitive to executive function deficits in the adult ADHD population. A second interpretation is that the sample size of this study was too small and the statistical power too low to detect a difference between groups. A related issue is the makeup of the clinical populations. In this study, participants consisted primarily of college students with ADHD (or DRD), whose ADHD symptoms may be less severe than the majority of the adult ADHD population. Clearly, college students with ADHD are not representative of the typical adult with ADHD, given that relatively few pursue a college education (Mannuzza et al., 1993). Nevertheless, this is an important subgroup of ADHD adults to study as information concerning these students is virtually nonexistent. Thus, the empirical question remains unexplored: whether subgroups of adults with ADHD exist, and whether they differ in executive function. Future research is also needed to (a) determine whether executive function deficits are characteristic of adults with ADHD and/or other disorders and to (b) identify neuropsychological tasks that can discriminate adults with ADHD from other clinical groups and controls. The second purpose of the study was to explore the psychometric properties of three ADHD rating scales designed for use with adults: ARS, WURS, and the PBC. Although numerous scales are available for children, little information is available concerning the psychometric properties of adult ADHD rating scales. Overall, results of this study supported the second hypothesis that the rating scales would differentiate groups. The findings support the psychometric of all three instruments, suggesting that they are measuring symptoms specific to ADHD rather than general psychological functioning. These results are consistent with previous research (Weyandt et al.,1995). Results from discriminant function analysis further support the clinical utility of the rating scales, as 67% of the cases were correctly classified. These results are encouraging as, at present, valid and reliable rating scales for use in the assessment of ADHD in adults are limited. Additional research is needed to determine whether the ARS, WURS, and PBC can reliably discriminate between adults with ADHD and other clinical disorders such as Depression and Anxiety Disorders; however, preliminary results support the use of these instruments in research and clinical settings as part of a comprehensive assessment protocol.

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Several limitations of this study should be noted. The first concerns the inclusionary criteria. To be included in the study, adults with ADHD and DRD were required to be registered with the ADA office or to present documentation of their diagnosis, and controls were screened to be certain they did not have a history of either disorder. Although the diagnoses were based on DSM-III-R criteria, it was impossible to control for differences in assessment procedures among the physicians and psychologists. Thus, despite efforts during recruitment to create "clean" groups, two participants reported a history of both ADHD and DRD. Future research may benefit from developing more stringent inclusionary criteria. A second limitation of the study is that 8 of the 21 ADHD participants were taking medication at the time of the study. Based on the ethical issues involved in requesting participants cease their medication, this variable was not controlled for (e.g., type, amount, and length of time). Although post hoc analyses did not suggest medication effects, the possibility remains that participants would have performed differently had they not been taking medication; thus, differences that might have emerged may have been obfuscated. Additional limitations include the small sample size, low statistical power, and restricted ADHD group. In conclusion, the results of this study support the psychometric properties of three adult ADHD rating scales, although additional research is warranted to further evaluate the clinical utility of these instruments. The study raises questions concerning the stability of ADHD symptoms in adults and the sensitivity of executive function tasks in detecting deficits in the adult ADHD population.

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