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This article was downloaded by: [University of Calgary]On: 19 August 2013, At: 08:16Publisher: RoutledgeInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK
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Neuropsychological Functioning of Adults withAttention Deficit Hyperactivity DisorderAlexandra Y. Walker , Arthur E. Shores , Julian N. Trollor , Teresa Lee & Perminder S.SachdevPublished online: 09 Aug 2010.
To cite this article: Alexandra Y. Walker , Arthur E. Shores , Julian N. Trollor , Teresa Lee & Perminder S. Sachdev(2000) Neuropsychological Functioning of Adults with Attention Deficit Hyperactivity Disorder, Journal of Clinical andExperimental Neuropsychology, 22:1, 115-124
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* This study was supported in part by funding from the University of New South Wales.Address correspondence to: Alexandra J. Walker, Neuropsychiatric Institute, Prince of Wales Hospital,Randwick, New South Wales, 2031, Australia. E-mail: [email protected] for publication: July 8, 1999.
Journal of Clinical and Experimental Neuropsychology 1380-3395/00/2201-115$15.002000, Vol. 22, No. 1, pp. 115-124 © Swets & Zeitlinger
Neuropsychological Functioning of Adults with AttentionDeficit Hyperactivity Disorder*
Alexandra J. Walker1, E. Arthur Shores2, Julian N. Trollor1,3,, Teresa Lee1,and Perminder S. Sachdev1,3
1Neuropsychiatric Institute, Prince of Wales Hospital, Sydney, Australia, 2Macquarie University, Sydney,Australia, and 3 School of Psychiatry, University of New South Wales, Australia, and Neuropsychiatric
Institute, Prince of Wales Hospital
ABSTRACT
The neuropsychological functioning of adults with Attention Deficit Hyperactivity Disorder (ADHD) wascompared to that of healthy controls and individuals with mild psychiatric disorders including attentionalcomplaints. Thirty adults in each group were examined on the Conners’ Continuous Performance Test(CPT) and measures of attention, executive function, psychomotor speed, and arithmetic skills. The ADHDgroup performed lower than healthy controls on most measures. However when compared to the psychia-tric group, the performances of the ADHD group were not significantly lower on any of the measures. Thepredictive power of the tests was poor in discriminating ADHD from psychiatric disorder. Implications forthe clinical diagnosis of ADHD are discussed.
Attention Deficit Hyperactivity Disorder(ADHD) is a commonly diagnosed disorder inchildren, with a reported prevalence of 3 to 5%in the general population (American PsychiatricAssociation, 1994). Of those with ADHD inchildhood, 30 to 50% continue to show symp-toms of the disorder in adulthood (Mannuzza etal., 1991). The Wender-Utah criteria are com-monly used in the diagnosis of ADHD in adults(Wender, Reimherr, & Wood, 1981). In additionto current symptoms of the disorder, thesecriteria require a retrospective diagnosis ofADHD in childhood, according to the criteria inthe Diagnostic and Statistical Manual-IV (Amer-ican Psychiatric Association, 1994).
Adults with ADHD show similarities to chil-dren with the disorder in terms of demographiccharacteristics, psychosocial functioning, andpsychiatric co-morbidity. There is an over-rep-resentation of males by three to one (Barkley,1997). The disorder is associated with poor so-
cial and marital relationships, employment in-stability, lower socio-economic status, and ahistory of learning disability and poor schoolachievement (Biederman et al., 1993). In addi-tion, ADHD has high levels of co-morbiditywith psychiatric conditions such as mood andanxiety disorders, substance abuse, and anti-so-cial and other personality disorders (Biedermanet al., 1993; Downey, Stelson, Pomerleau, &Giordani, 1997). As many as 50% of adults withADHD may have a co-morbid psychiatric diag-nosis (Downey et al., 1997).
The neuropsychological functioning of indi-viduals with ADHD has been extensively stud-ied in childhood. Children with the disorder dis-play response disinhibition, inattention, and highvariability in response speed on continuous per-formance testing (Barkley & Grodzinsky, 1994).They also show executive dysfunction charac-terised by poor interference control, mental in-flexibility, reduced verbal fluency, and limited
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116 ALEXANDRA J. WALKER ET AL.
abstracting ability (Barkley & Grodzinsky,1994; Barkley, Grodzinsky, & DuPaul, 1992).Finally, their information processing and psy-chomotor speeds are slowed and arithmeticskills are reduced (Barkley et al., 1992). Theabove findings are consistent with demonstratedfrontal lobe abnormalities on neuroimagingstudies, and suggest that ADHD may be in partcharacterized by an impairment in frontally-me-diated executive and attentional functions(Barkley, 1997).
Whereas the above profile of impaired neuro-psychological function has emerged from stud-ies of ADHD in children, such impairments havenot been established in adults. Despite the pro-liferation of research into ADHD over the lastdecade, there has been limited research into thecognitive functioning of adults with the disorder(Tannock, 1998). The findings of this limitedresearch have been inconsistent. For example,response inhibition on continuous performancetesting has shown impairment in some studies(Arcia & Gualtieri, 1994; Klee, Garfinkel, &Beauchesne, 1986) but not in others (Downey etal., 1997; Holdnack, Moberg, Arnold, Gur, &Gur, 1995; Matochik, Rumsey, Zametkin, Ham-burger, & Cohen, 1996). A consistent finding oncontinuous performance testing is higher levelsof inattention, indicated by more omissions, andresponse speed variability (Arcia & Gualtieri,1994; Downey et al., 1997; Holdnack et al.,1995; Klee et al., 1986). However, findings inother areas such as immediate memory span,working memory span, and psychomotor speedare inconsistent (Holdnack et al., 1995; Mato-chik et al., 1996; Silverstein, Como, Palumbo,West, & Osborn, 1995, but not Downey et al.,1997). Some studies have found reduced arith-metical skills in adult ADHD (Biederman et al.,1993), whereas others have not (Matochik et al.,1996). Finally, aspects of executive function,such as verbal fluency, show reduction in somestudies (Jenkins et al., 1998), but not in others(Holdnack et al., 1995).
The above inconsistencies within researchfindings on the neuropsychological functioningof adults with ADHD may partly result from arange of methodological problems (Barkley,1997). First, appropriate instruments, such as
tests of continuous performance to detect diffi-culties in sustaining attention over time, werenot always administered (e.g., Biederman et al.,1993; Silverstein et al., 1995). Second, perfor-mances were not always compared to a controlgroup (e.g., Downey et al., 1997; Matochik etal., 1996). In one such study, in which testscores of the ADHD group were compared tonormative data, the ADHD group was of aboveaverage intelligence, which may have accountedfor the negative findings (Matochik et al., 1996).Third, where a control group was used, thegroups were not always matched on levels ofintelligence and education (e.g., Roy-Byrne etal., 1997).
Further methodological problems have re-lated to subject selection. First, the Wender-Utah criteria for the diagnosis of ADHD werenot always adhered to, in terms of requiring ret-rospective diagnosis of ADHD in childhood(e.g., Arcia & Gualtieri, 1994). In this regard, ithas been shown that the cognitive profile ofadults with ADHD is different to that of adultswith attentional complaints without a childhoodhistory of ADHD (Jenkins et al., 1998). Second,most studies failed to control for psychiatric co-morbidity (e.g., Jenkins et al., 1998; Roy-Byrneet al., 1997). Such a failure leads to a potentialconfounding of results in terms of attributingany deficits solely to a primary attentional disor-der, given that depression and anxiety may alsoimpair attentional and executive functions(Brand & Jolles, 1987). In fact, adults withADHD and co-morbid psychiatric diagnoseshave been shown to perform more poorly onneuropsychological tests than those with pureADHD (Downey et al., 1997). Finally, despitethe high co-morbidity of ADHD with substanceabuse, which is known to be associated withneuropsychological deficits (Hoegerman,Resnick, & Schnoll, 1993), some studies havefailed to screen for a significant history of pastor current substance use (e.g., Roy-Byrne et al.,1997).
The methodological problems describedabove may well account for the failure of exist-ing research to establish the neuropsychologicalprofile of ADHD in adults. The establishment ofsuch a profile would appear to be crucial, how-
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ATTENTION DEFICIT DISORDER IN ADULTS 117
ever, for validating ADHD as a neurocognitivedisorder. Given that ADHD in adults is under-stood as a continuation of a developmental dis-order, the cognitive profile would be expected toshow some similarity to that in childhood, al-lowing for some differences due to brain matu-ration processes. Furthermore, the areas of neu-ropsychological dysfunction should be related toabnormalities in underlying brain substrates,such as the orbitofrontal region, which havebeen demonstrated in imaging studies (Tannock,1998). Finally, the delineation of the cognitiveprofile in ADHD is important in validating theuse of a neuropsychological examination in clin-ical settings. As noted above, the impairments inexecutive and attentional functions related toADHD have also been associated with psychiat-ric disorders such as depression and anxiety(Brand & Jolles, 1987). It is therefore importantto examine the specificity of the neuropsycho-logical deficits in ADHD with a view to differ-entiating the disorder from psychiatric problems(Jenkins et al., 1998).
The present study aimed to address the aboveissues in an examination of the neuropsycholog-ical function of adults with ADHD. Comparisonwas made with a healthy control group and apsychiatric group. It was hypothesised that rela-tive to healthy controls, adults with ADHDwould show impairments on measures of atten-tional and executive function such as responseinhibition, interference control, response speedvariability, working memory, verbal fluency,and speed of information processing, as well asarithmetical skills. Given that a profile of neuro-psychological deficits in ADHD would emerge,it was then planned to examine its specificity viacomparison with the psychiatric group. Finally,the predictive power of the tests in terms of theirability to predict group membership would beexamined.
METHOD
ParticipantsThere were 30 participants in each of three groups:ADHD, psychiatric and healthy controls. Partici-pants were aged between 17 and 50 years. The in-
dividuals in the ADHD and psychiatric groups at-tended an outpatient clinic for the assessment ofADHD in adults. The 30 healthy controls were re-cruited from the community and were paid fortheir participation. The hospital’s Ethics Commit-tee approved the study.
Individuals with a significant history of past orcurrent substance abuse, loss of consciousness ofover 5 min, epilepsy or other neurological event orprocess were excluded. People with an estimatedborderline or lower intellectual level or a history oflearning difficulties were also excluded, as werethose who had not attended school in Australia.Participants in the control group were alsoscreened for past or present attentional disorders,mood and anxiety disorders, and other major psy-chiatric disorders.
Individuals in the ADHD and psychiatric groupswere referred to the clinic with attentional com-plaints as well as other possible indicators ofADHD. The clinic assessment comprised a de-tailed patient and informant interview with a Con-sultant Psychiatrist, completion of rating scalesand psychological inventories, and review ofschool reports where possible. Diagnosis was byconsensus with two Psychiatrists (JT, PS) and twoClinical Psychologists (AW, TL). The ADHDgroup met Wender-Utah criteria for ADHD, in-cluding current symptoms and the retrospectivediagnosis of childhood ADHD according to DSM-IV criteria. Individuals with ADHD who also metDSM-IV criteria for either an Axis I psychiatricdisorder (10 individuals with anxiety, mood, orsubstance-related disorders) or an Axis II disorder(6 with anti-social or borderline personality disor-ders) were excluded. One person currently takingstimulant medication was also excluded. The psy-chiatric participants did not meet criteria forADHD, either currently or in childhood. They didmeet DSM-IV criteria for a psychiatric disorder.There were 15 individuals with mood disorders, 10with anxiety disorders, and 5 with mixed mood andanxiety disorders.
ProcedureAll participants completed a standardised neuro-psychological assessment with a Clinical Psychol-ogist. Tests were selected on the basis of measuresthat have demonstrated sensitivity to ADHD inprevious research. The assessment was designed tomeasure: estimated intelligence-National AdultReading Test, Revised, (NART-R; Crawford,1992); attentional variables-Conners ContinuousPerformance Test (CPT; Conners, 1992), DigitSpan, Wechsler Adult Intelligence Scale, Revised(WAIS-R; Wechsler, 1981); psychomotor speed-
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Table 1. Demographic Data.
ADHD Psychiatric Controls F(2, 87)a
n n nb
Gender (M/F) (25/5) (21/9) (20/10)
M (SD) M (SD) M (SD)
AgeEducationNART-R, FSIQWAIS-R, InfoBDISTAI-1STAI-2WURS
25.811.095.017.211.343.947.964.6
(8.7)(2.0)(8.3)(6.1)
(10.5)(11.1)(11.7)(17.0)
35.110.798.119.119.051.158.353.2
(8.4)(1.8)(9.3)(5.6)(9.8)
(14.0)(9.1)
(18.3)
25.811.499.819.8
4.530.632.9
N/A
(6.8)(1.0)(9.5)(5.8)(4.4)(6.9)(8.0)
13.29***1.352.211.59
20.84***26.30***50.67***
5.84*c
Note. ADHD = Attention Deficit Hyperactivity Disorder group; NART-R = National Adult Reading Test, Re-vised; WAIS-R, Info = Information subtest of Wechsler Adult Intelligence Scale, Revised; BDI = Beck Depres-sion Inventory; STAI-1, STAI-2 = State-Trait Anxiety Inventory, Parts 1 & 2; WURS = Wender Utah RatingScale; N/A = not administered.a One-way between-subjects ANOVA, sample characteristics (except for gender) as dependent variables, post hoccomparisons where significant differences found. An alpha value of .05 was used for all statistical analyses.b Chi-square analysis (3 × 2, group × gender) P2(2, N = 90) = 2.39, p < 0.10.c WURS not administered to controls, DF = 1, 54.* p < .05; **p < .01; ***p < .001.
Digit Symbol, WAIS-R, Trail Making Test,(Lezak, 1995); arithmetic skills-Arithmetic,WAIS-R; executive function-Controlled OralWord Association Test (COWAT), animal fluency(Lezak, 1995), Stroop Test (Golden, 1978); psy-chological state-depression-Beck Depression In-ventory (BDI; Beck & Steer, 1987), anxiety-State-Trait Anxiety Inventory (STAI; Speilberger, Go-rusch, & Lushene, 1970); and self-reported ADHDsymptoms – Wender Utah Rating Scale (WURS;Ward, Wender, & Reimherr, 1993).
RESULTS
Sample CharacteristicsSample characteristics and results of tests ofsignificant differences across groups aresummarised in Table 1. The groups were notstatistically different by gender. The psychiatricgroup was significantly older than both thehealthy control and ADHD groups. Years of ed-ucation, estimated Full Scale Intelligence Quo-tient on the NART-R and WAIS-R Informationraw score were not statistically different. Statis-
tically significant effects were demonstrated fordepression rating on BDI and anxiety ratings onSTAI-1 and STAI-2. On these three measures,the psychiatric group was higher than the ADHDgroup who in turn was higher than the healthycontrol group. The effect of self-reported ADHDsymptoms on the WURS was statistically signif-icant, with the ADHD group scoring morehighly than the psychiatric group.
Group Comparisons on NeuropsychologicalMeasuresNeuropsychological data were subjected first tomultivariate analysis of covariance, with onebetween-subjects independent variable, groupwith three levels, and one covariate, age. The 18neuropsychological variables were entered asdependent variables. There was a significantmain effect for group, F(2, 86) = 2.07, p < .01.Subsequent univariate analyses of covariancerevealed that age was significant only for arith-metic, F(2, 86) = 3.80, p < .001.
Given that the above multivariate analysis ofcovariance was significant, univariate analyses
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ATTENTION DEFICIT DISORDER IN ADULTS 119
Table 2. Neuropsychological Tests Results.
ADHD Psychiatric Control t(87)a t(87)b
M (SD) M (SD) M (SD)
OmissionCommissionHitRT (ms)RT SE (ms)ISI RT chOvindexArithmeticDSymbolDForwardDBackwardCOWATAnimalTMTA (s)TMTB (s)Stroop, wordStroop, colStroop, c/wStroop, intf
6.217.6354.0
7.20.076.49.9
46.98.45.6
31.918.830.580.686.060.533.4–1.7
(6.8)(7.8)
(61.2)(3.6)
(.04)(5.9)(3.2)
(13.2)(2.6)(1.7)(8.9)(3.8)(9.7)
(23.8)(14.5)(8.6)(6.5)(5.3)
2.814.1360.2
6.10.053.6
10.354.3
8.56.0
34.820.029.083.790.165.136.4–0.4
(3.4)(7.6)
(54.8)(1.9)
(.04)(4.9)(3.5)
(11.4)(2.8)(2.1)(8.8)(3.9)(8.9)
(36.2)(15.0)(10.1)(8.6)(8.2)
1.69.4
365.94.90.052.3
12.162.0
9.07.2
41.723.326.762.0104.472.746.0
3.1
(0.9)(5.7)
(73.5)(1.8)
(.03)(4.7)(3.1)(8.4)(2.6)(2.1)
(13.2)(5.7)
(10.6)(18.7)(18.5)(12.5)(8.1)(6.5)
4.05*4.48*0.723.49*2.493.02*2.595.23*0.963.11*3.60*3.83*1.492.654.45*4.53*6.25*2.77
3.001.910.381.652.142.060.472.580.190.731.061.000.580.441.001.691.470.76
Note. ADHD = Attention Deficit Hyperactivity Disorder group; Omission = number of omissions on ContinuousPerformance Test (CPT); Commission = number of commissions, CPT; HitRT (ms) = mean hit reaction time(milliseconds, CPT); RT SE (ms) = hit standard error RT (milliseconds, CPT); ISI RT ch = change in reactiontimes over three interstimulus intervals, CPT, positive value indicates slowing of RT as time between stimuliincreased; Ovindex = overall index on CPT; WAIS-R = Wechsler Adult Intelligence Scale, Revised; Arithmetic= Arithmetic raw score, WAIS-R; DSymbol = Digit Symbol raw score, WAIS-R; DForward = digits forwards rawscore on Digit Span, WAIS-R; DBackward = digits backwards raw score on Digit Span, WAIS-R; COWAT =Controlled Oral Word Association Test, total words; Animal = number of animals in 1 min; TMTA = TrailMaking Test, Part A (s); TMTB = Trail Making Test, Part B (s); Stroop, word = Stroop Colour and Word Test,words; Stroop, col = Stroop Colour and Word Test, colours named; Stroop, c/w = Stroop Colour and Word Test,interference task, colours named; Stroop, intf = Stroop Colour and Word Test, interference score.a Planned comparisons, ADHD & healthy controls.b Planned comparisons, ADHD & psychiatric group.* p < .003.
with planned comparisons were then performedfor each of the neuropsychological variables. Aconservative alpha level of .003 was used forbetween-group statistical analyses to adjust forthe number of tests performed. First, the ADHDgroup and healthy controls were compared,based on a priori assumptions that the ADHDgroup would perform more poorly on measuresof response inhibition, interference control, re-sponse speed variability, working memory, ver-bal fluency, speed of information processing,and arithmetical skills. The ADHD group wasthen compared to the psychiatric group. Resultsof these analyses are summarised in Table 2.The ADHD group scored significantly more
poorly than the healthy control group on mostCPT indices (number of omission and commis-sion errors, response speed variability, overallindex). They also performed more poorly onmental and psychomotor performance speed(Digit Symbol, Stroop tasks), working memory(Digits Backwards), and verbal fluency(COWAT, animals). Overall, 11 significant dif-ferences were found on the 18 neuropsychologi-cal variables.
Comparison of the ADHD and psychiatricgroups revealed no significant differences onany of the 18 measures. Inspection of the meansfor the two groups revealed that although nomeasures reached significance, there was a trend
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120 ALEXANDRA J. WALKER ET AL.
Table 3. Logistic Regression Analysis for Neuropsychological Variables Predicting Diagnosis of ADHD andHealthy Controls (n = 60).
Measure B Wald testChi-square
Odds ratio 95% CI for odds ratio
Lower Upper
CommissionRT SE (ms)Stroop, c/wDSymbol
-0.25-0.810.250.12
8.70**4.33*7.15**2.53
0.780.451.131.28
0.660.211.070.97
0.920.951.531.32
Note. ADHD = Attention Deficit Hyperactivity Disorder group; Commission = number of commissions on Con-tinuous Performance Test (CPT); RT SE = hit standard error RT (time) on CPT; Stroop, c/w = Stroop Colour andWord Test, interference task, colours named; DSymbol = Digit Symbol raw score, Wechsler Adult IntelligenceScale, Revised.* p < .05; ** p < .01.
for poorer performances within the ADHDgroup on all measures. Those measures that ap-proached significance were number of omissionsand psychomotor speed (Digit Symbol).
In order to determine the power of the neuro-psychological variables to predict group mem-bership, step-wise logistic regression analysiswas performed. Inclusion of variables into themodel was based on a liberal alpha of .15 in or-der to maximise predictive accuracy. First,membership of the ADHD or healthy controlgroup was assessed on the basis of those neuro-psychological measures on which the twogroups differed. These measures were CPT indi-ces (number of omission and commission errors,response speed variability, overall index), men-tal and psychomotor performance speed (DigitSymbol, Stroop tasks), working memory (DigitsBackwards), and verbal fluency (COWAT, ani-mals). A model with four predictors was derivedand a test of this model entered against a con-stant only model was statistically reliable P2(4, n= 60) = 57.54, p < .0001. The predictors enteredin the model were: number of commission er-rors, reaction time variability, colour-word scoreon the Stroop, and Digit Symbol score. Predic-tion success was good, 93% of the ADHD group(sensitivity) and 90% of the healthy controls(specificity) were classified correctly. Table 3shows regression coefficients, Wald statistics,odds ratios, and 95% confidence intervals forodds ratios for each of the four predictor vari-ables.
A second step-wise logistic regression wasperformed to assess prediction of ADHD andpsychiatric group membership, on the basis ofthose neuropsychological measures that ap-proached a significant difference betweengroups. These measures were omissions, re-sponse speed change with interstimulus interval,overall index, and Digit Symbol. Three predictormeasures were entered into the model. A test ofthis model against a constant only model wasstatistically reliable, P 2 (5, n = 60) = 13.62, p <.01. The predictor variables were number ofomissions, response speed change withinterstimulus interval, and psychomotor speedon Digit Symbol. Prediction success was poor,63% of the ADHD group (sensitivity) and 80%of the psychiatric controls (specificity). Table 4shows regression coefficients, Wald statistics,odds ratios, and 95% confidence intervals forodds ratios for each of the three predictor vari-ables.
Given the relatively poor predictive power ofthe above model, a further step-wise logisticregression was performed to assess prediction ofADHD and psychiatric group membership, onthe basis of rating scales of depression, anxiety,and ADHD symptoms, as well as neuropsycho-logical variables. In this model four variableswere entered. A test of this model against a con-stant only model was statistically reliable, P 2 (5,n = 53) = 29.19, p < .0001. The predictor vari-ables were number of omissions, response speedchange with interstimulus interval, anxiety rat-
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ATTENTION DEFICIT DISORDER IN ADULTS 121
Table 5. Logistic Regression Analysis for Neuropsychological Variables and Rating Scales Predicting Diagnosisof ADHD and Psychiatric Group (n = 53).
Variables B Wald testChi-square
Odds ratio95% CI for odds ratio
Lower Upper
OmissionISI RT chSTAI-2WURS
–0.20-25.72
0.12–0.03
3.543.829.21**5.45*
0.820.001.130.94
0.670.001.040.90
1.011.071.230.99
Note. ADHD = Attention Deficit Hyperactivity Disorder group; Omission = number of omissions, ContinuousPerformance Test (CPT); ISI RT ch = change in reaction times over three interstimulus intervals on CPT, positivevalue indicates slowing of RT as time between stimuli increased; STAI-2 = State-Trait Anxiety Inventory, part2; WURS = Wender Utah Rating Scale.* p < .05; ** p < .01.
Table 4. Logistic Regression Analysis for Neuropsychological Variables Predicting Diagnosis of ADHD andPsychiatric Group (n = 60).
Variables B Wald testChi-square
Odds ratio 95% CI for odds ratio
Lower Upper
OmissionISI RT chDSymbol
–0.13–18.14
0.04
3.023.96*2.41
0.880.001.04
0.760.000.99
1.020.771.10
Note. ADHD = Attention Deficit Hyperactivity Disorder group; Omission = number of omissions, ContinuousPerformance Test (CPT); ISI RT ch = change in reaction times over three interstimulus intervals on CPT, positivevalue indicates slowing of RT as time between stimuli increased; DSymbol = Digit Symbol raw score, WechslerAdult Intelligence Scale, Revised.* p < .05.
ing on STAI-2, and self-reported symptoms ofADHD on the WURS. Predictive success wasconsiderably improved, giving a sensitivity of81% for ADHD and a specificity of 85%. Table5 shows regression coefficients, Wald statistics,odds ratios, and 95% confidence intervals forodds ratios for each of the four predictor vari-ables.
Whereas the above analyses examined thepredictive power of the neuropsychological vari-ables as a whole, as well as in combination withrelevant rating scales, the predictive power of asingle measure, such as omissions on CPT, wasalso of interest. Inspection of the number ofomissions revealed that a cut-off point of two orgreater as positive for ADHD would optimallyclassify the ADHD and non-ADHD groups.
Thus a score of two or more omissions wasdeemed positive for ADHD, and less than twoomissions was negative for the diagnosis; theresultant classifications are shown in Table 6.Diagnostic efficiency statistics were then calcu-lated given base rates of 50%, for participantswith ADHD and healthy controls and then forthe ADHD and psychiatric groups. These statis-tics with their 95% confidence intervals are dis-played in Table 7.
DISCUSSION
The present results demonstrate that the neuro-psychological functioning of adults with ADHDmay be impaired on a range of executive and
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122 ALEXANDRA J. WALKER ET AL.
Table 7. Diagnostic Efficiency Statistics and Confidence Intervals, Using Two or More Omissions on CPT asPositive for ADHD, Given Base Rates of 50%, for ADHD and Controls, and ADHD and PsychiatricGroup.
ADHD & controls ADHD & psychiatric
Statistic Value (%) 95% CI Value (%) 95% CI
SensitivitySpecificityPositive predictive powerNegative predictive power
63908671
44-8873-9965-9754-85
63606167
44-8841-7742-7842-79
Table 6. Classification of Groups (ADHD or Non-ADHD) Using Two or More Omissions on CPT as Positive forADHD.
Number of omissions ADHD Diagnosis Non-ADHD(Psychiatric)
Non-ADHD(Controls)
2< 2
1911
1218
1327
Note. CPT = Continuous Performance Test (CPT); ADHD = Attention Deficit Hyperactivity Disorder.
attentional measures when compared to healthycontrols. However, these impairments may notbe evident in comparison to the neuropsycholog-ical functioning of individuals with mild depres-sive and anxiety disorders who also complain ofpoor attention. Also, selected neuropsychologi-cal tests may have high sensitivity and specific-ity to ADHD when compared to that of healthycontrols. However, the sensitivity and specific-ity of these tests may be unacceptably low whendistinguishing adults with ADHD from thosewith mild depressive and anxiety disorders. Im-proved prediction of ADHD within the lattergroups may require the addition of measures ofdepression, anxiety, and self-reported ADHDsymptoms.
The ADHD group displayed attentional andexecutive dysfunction relative to healthy con-trols. Specifically, on a Continuous PerformanceTest they displayed poor response inhibition(commission errors), inattention (omission er-rors), and inconsistency of response latency(high variability of reaction time). The ADHDgroup was also slower on tests of psychomotorperformance and mental speed (Digit Symbol,Stroop Test). They scored lower on verbal flu-
ency (COWAT, animal fluency) and workingmemory (Digits Backwards). Adults withADHD were able to attend to tasks of brief dura-tion, such as auditory immediate memory span,but were unable to consistently sustain attentionover longer intervals. The slowing displayed ontimed tasks was not related to motor speed,given that no differences were found on reactiontime and simple tracking, but reflected an im-pairment in speed of information processing.
Adults with ADHD displayed a range of im-pairments relative to healthy controls, yet incomparison to people with mild depressive andanxiety disorders, their performances were notsignificantly poorer on any of the measures.Those measures that approached significancewere inattention as measured by omissions onCPT and psychomotor slowing on Digit Symbol.There was a trend on all measures for the milddepressive and anxiety disorders group to per-form better than the ADHD group, but below thelevel of the healthy controls. The reduced per-formance of the psychiatric group relative tocontrols was not related to intelligence or educa-tion, on which the groups were similar. Al-though participants in the psychiatric group
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were older, age was significant only in relationto arithmetic skills. It appeared then that theirlower performance was associated with theirpsychiatric disorder. Given that they were pre-senting with attentional complaints, they may bean atypical subset of those individuals with milddepressive and anxiety disorders.
The degree of impairment of the ADHDgroup was relatively mild. When compared toappropriate normative data, scores of one stan-dard deviation or more below the mean wereobtained on four measures only. These were in-attention and increased response latency withslower stimulus presentation on continuous per-formance testing, and slowed information pro-cessing on Trails B and Stroop tasks.
The results overall suggest that the mostprominent features of the neuropsychologicalfunction of the ADHD group were inattentionand slowed information processing. Similarfindings have been reported in previous re-search, and inattention as measured by omis-sions on CPT is one of the few consistent find-ings in the literature (Downey et al., 1997).Therefore, it may be that inattention is a keyfeature in adult ADHD, whereas response disin-hibition is the more prominent feature in child-hood. Should such a progression be established,it may reflect the influence of maturational pro-cesses, particularly the development of the fron-tal lobes. Children with ADHD displayimpulsivity in both everyday life and on neuro-psychological testing, but adults with the disor-der may be more able to inhibit their behaviourin structured situations such as that of formaltesting. These findings suggest that inattentionand slowed information processing may be theprimary residual neuropsychological impair-ments in adulthood.
The sensitivity and specificity of the neuro-psychological tests as a group were poor in theclinical comparison groups. Reliance on suchtest results would lead to false positives innearly one quarter of the psychiatric group andfalse negatives in one third of ADHD cases. Thediagnostic efficiency of a single test index, suchas the number of omission errors on the CPTwas even lower, with a positive predictive powerof 61% and negative predictive power of 67%,
given the base rate of 50%. Such findings pointto the need to assess psychiatric symptoms, andlevels of anxiety and depression, and in caseswhere they are significant, to use caution in di-agnosing ADHD. In fact diagnosis may need tobe deferred until after appropriate treatment forthe psychiatric disorder. In addition, the lowsensitivity of neuropsychological tests meansthat there is a high probability of missing thediagnosis of ADHD in those individuals withnormal neuropsychological functioning. In suchcases, where high levels of self-reported symp-toms of ADHD are present, the diagnosis wouldneed to be considered. This underlines the needto include such measures as an adjunct to neuro-psychological testing.
The present findings need to be viewed aspreliminary, given the relatively small samplesize. These findings require replication with alarger sample. The neuropsychological measuresemployed in the current study were focussed onmeasures of attention and executive function.Given that memory dysfunction on more com-plex tasks has also been shown in this group,such tests should also be included with a view toimproving sensitivity (Holdnack et al., 1995).The inconsistency of research findings in thisarea points to the need for further research inwhich issues of diagnosis and co-morbidity arecarefully examined. On the basis of the presentresults, such studies should include measures ofanxiety, depression, and self-reported attentionalsymptoms as well as appropriate neuropsycho-logical measures. Finally, longitudinal researchis needed to chart areas of neuropsychologicaldysfunction from childhood to adulthood, with aview to establishing changes in the primary fea-tures of the disorder due to brain maturationalprocesses.
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