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Effects of Comorbid ADHD with Learning Disabilities on Anxiety, Depression, and Aggression in
Adults
J.A. McGillivray and K.L. Baker
J Atten Disord 2009; 12; 525 originally published online Jul 2, 2008;
DOI: 10.1177/1087054708320438
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Effects of Comorbid ADHD With Learning
Disabilities on Anxiety, Depression, and
Aggression in Adults
Journal of Attention Disorders
Volume 12 Number 6
May 2009 525-531
© 2009 SAGE Publications
10.1177/1087054708320438
http://jad.sagepub.com
hosted at
http://online.sagepub.com
J. A. McGillivray
K. L. Baker
Deakin University, Victoria, Australia
Objective: ADHD and learning disabilities (LD) frequently coexist and there are indications that comorbidity may increase
the risk of psychopathology. Method: The current study examined the gender distribution and frequency of comorbidity
and its impact on the prevalence of symptoms of anxiety, depression, and aggression in a clinic sample of 80 adults with
ADHD, aged 18 to 58 years. More individuals were diagnosed with ADHD+LD than ADHD only, with no difference in this
distribution according to gender. Results: A factorial multivariate analysis of variance indicated that females with
ADHD+LD displayed more cognitive depression than females with ADHD only and than males with ADHD+LD and
ADHD only. However,individuals with ADHD only and individuals with ADHD+LD did not differ on overall anxiety,
depression or aggression. Likewise, males and females did not differ on measures of psychopathology. Conclusion: This
study lays the foundation for continued research into the characteristics and comorbidities of adults with ADHD. (J. of Att.
Dis. 2009; 12(6) 525-531)
Keywords:
A
ADHD; learning disabilities; comorbidity; depression; adults
DHD is one of the most common childhood disorders with behavioral and cognitive difficulties generally emerging before the age of 7 years (American
Psychiatric Association, 2000). More recently, however,
ADHD has been found to appear later in childhood or
mid-adolescence (Rohde et al., 1999; Willoughby,
Curran, Costello, & Angold, 2000), and to persist into
adulthood in 30% to 90% of childhood cases (e.g., Adler,
2004; Bellak & Black, 1992; Biederman et al., 2006;
Biederman, Mick, & Faraone, 2000; Faraone, Biederman,
Feighner, & Monuteaux, 2000). Although these findings
have prompted increased attention, further research is
needed to clarify the prevalence and correlates of ADHD
in adults (Kessler et al., 2006).
High rates of comorbidity have been reported within
the ADHD population in both epidemiological and clinical samples (e.g., Adler, Sitt, Nierenberg, & Mandler,
2006; Biederman et al., 1993; Biederman, Newcorn, &
Sprich, 1991; Kollins, 2007; Mayes, Calhoun, &
Crowell, 2000). ADHD frequently coexists with learning
disabilities (LD; e.g., Mayes et al., 2000), with disruptive
behavior disorders including conduct disorder (CD) and
oppositional defiant disorder (ODD; e.g., Biederman et
al., 1993; McGough et al., 2005), and with psychopathologies such as anxiety and depression (e.g.,
Adler et al., 2006; Lomas & Gartside, 1997; McGough
et al., 2005). Although prevalence varies with the diagnostic criteria used (Epstein, Shaywitz, Shaywitz, &
Woolston, 1991), high lifetime prevalence rates of
comorbidity are reported in both children and adolescents (44% to 86%; Kuhne, Schachar, & Tannock, 1997;
Newcorn et al., 2001; Rucklidge & Tannock, 2001), as
well as in adults (40% to 82%; Biederman et al., 1993;
Milberger, Biederman, Faraone, Murphy, & Tsuang,
1995). Patterns of psychopathology appear similar
across age groups, suggesting that the findings from
childhood studies can serve as a foundation for comorbidity research in adults with ADHD (Biederman et al.,
1993).
Authors’ Note: Address correspondence to Dr. Jane McGillivray,
School of Psychology, Deakin University, 221 Burwood Highway,
Burwood, Victoria 3125, Australia; phone: +61 3 92446426; fax: +61
3 92446858; e-mail: [email protected].
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525
526 Journal of Attention Disorders
Researchers have described a strong link between
ADHD and LD (Javorsky, 1996; Jensen, Martin, &
Cantwell, 1997). Although the diagnostic criteria presents clear distinctions between the core symptoms of
ADHD and LD (American Psychiatric Association,
2000), certain features and disorders associated with
both ADHD and LD can cause the boundaries to become
blurred (Jensen et al., 1997). Symptom similarities
between the disorders include problems with inattention
and hyperactivity, low frustration tolerance, poor selfesteem, low morale, deficits in social skills, impaired
academic achievement, increased school drop out and
poor vocational achievement (American Psychiatric
Association, 2000; Epstein et al., 1991; Jensen et al.,
1997). As a result of overlapping symptoms, individuals
are often diagnosed with a comorbid ADHD and LD
condition (ADHD+LD).
There is widespread evidence that both individuals with
ADHD and individuals with LD are at risk for concomitant emotional and behavioral difficulties, such as anxiety,
depression, and aggression. For example, individuals with
ADHD have been found to experience elevated rates of
anxiety (2 to 4 times), depression (2 to 6 times), and
aggression when compared with control populations
(Biederman et al., 1991; Biederman et al., 1993). Anxiety
has been found to coexist with ADHD in 20% to 50% of
adult cases (Biederman et al., 1993; Milberger et al.,
1995), whereas depression has been found to occur with
ADHD in 8% to 44% of adult cases (Biederman et al.,
1993; Lomas & Gartside, 1997; Milberger et al., 1995).
ADHD is also commonly associated with disruptive
behavior disorders such as ODD and CD (e.g., Rapport,
Scalan, & Denney, 1999). In adults with ADHD, the
prevalence rates for coexisting ODD and CD range from
29% to 53% and 20% to 53%, respectively (Biederman
et al., 1993). High correlations between disruptive
behavior disorders and variables relating to aggression
have been documented (Hudziak, Rudiger, Neale, Heath,
& Todd, 2000; Mayes et al., 2000). Research by Rapport
et al. (1999) has also indicated that individuals with
ADHD may be particularly prone to aggressive and
delinquent behaviors.
Studies have also demonstrated a link between LD
and measures of anxiety (e.g., Bender & Wall, 1994;
Cantwell & Baker, 1991; Fisher, Allen, & Kose, 1996),
depression (e.g., Hoy et al., 1997) and disruptive behavior disorders/aggression (e.g., Church, Lewis, &
Batshaw, 1997; Javorsky, 1996). The reported prevalence
of comorbid ODD, CD, depression, and anxiety ranges
between 10% to 25% in individuals diagnosed with a LD
(American Psychiatric Association, 2000; Cantwell &
Baker, 1991).
The apparent elevated risk for concomitant emotional
and behavioral difficulties in both individuals with ADHD
and individuals with LD suggests that individuals with the
comorbid condition of ADHD+LD may be at even greater
risk of anxiety, depression, and aggression symptomatology than individuals with ADHD only. This contention
has some support in the literature. For example, the
ADHD+LD condition has been linked with a negative
prognosis with regard to cognitive, academic, and behavioral development (Church et al., 1997; Pisecco, Baker,
Silva, & Brooke, 2001), as well as social and emotional
development (Bender & Wall, 1994; Biederman et al.,
1993). However, further investigation is required (Bender
& Wall, 1994; Livingston, Dykman, & Ackerman, 1990),
particularly with respect to adult populations.
The impact of gender in individuals with ADHD is
also in need of clarification. ADHD is more often diagnosed in males, with male-to-female ratios varying from
3 to 1 in epidemiological studies and 9 to 1 in clinical
populations (Arcia & Conners, 1998). The diagnostic
rate for adults with ADHD, however, has been reported
to be equally divided among men and women
(Biederman, 2004). Gender-based comparisons are limited. There are indications that females may be somewhat less likely to receive a dual diagnosis of
ADHD+LD. In a study of 153 boys and 29 girls with
ADHD, for example, Livingston et al. (1990) reported
that the sample comprised 59% ADHD only (48% boys
and 11.5% girls) and 41% ADHD+LD (35.6% boys and
5.2% girls). In a study by Javorsky (1996), the
ADHD+LD sample consisted of only male children and
adolescents, whereas females comprised approximately
half the ADHD only group.
The evidence relating to gender differences in vulnerability to further psychiatric diagnoses in individuals with
ADHD remains equivocal. In a study of a clinical population of individuals with ADHD, Rucklidge and Tannock
(2001) reported that females were more impaired than
their male counterparts on measures of distress, anxiety,
depression, CD, ODD, and cognitive problems. In contrast, a meta-analysis of literature on gender differences
in children with ADHD undertaken by Gaub and Carlson
(1997) demonstrated that girls with ADHD display significantly lower levels of anxiety, depression, aggression,
and CD than boys. In addition, Carlson, Tamm, and Gaub
(1997) found significantly lower levels of aggression in
girls than boys with ADHD, and Biederman et al. (2002)
reported that girls with ADHD were at less risk for
comorbid major depression than boys.
In reference to gender differences in psychiatric
symptoms in the ADHD+LD population, Livingston
et al. (1990) found that only 17% of girls were likely to
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McGillivray, Baker / ADHD and Learning Disabilities 527
be diagnosed with anxiety and depression in comparison
to nearly 48% of boys. However, the likelihood of an
additional diagnosis of ODD and CD was equally prevalent in girls (38%) and boys (41%). There remains a need
for further research to clarify any gender differences in
susceptibility to additional diagnoses in ADHD and
ADHD+LD populations.
The frequent comorbidity of ADHD+LD is well established. In contrast, research into the characteristics of
adults with ADHD and ADHD+LD remains equivocal.
The question of whether adults with ADHD+LD have
higher rates of additional diagnoses in comparison to
adults diagnosed with ADHD only is yet to be determined
and the impact of gender also requires clarification.
Method
Participants
The sample was composed of 80 adults diagnosed
with ADHD (43 males and 37 females) ranging in age
from 18 to 58 years (M = 32.45 years, SD = 9.44) and
with a full-scale IQ (FSIQ) of 70 or above on the
Wechsler Adult Intelligence Scale–Revised (WAIS-R;
Wechsler, 1981) or the WAIS-III (Wechsler, 1997). Sixtyeight percent of participants had also been diagnosed with
a learning disability (27 males and 27 females). Participants
included 16 male ADHD (M = 31.63 years of age,
SD = 11.55), 10 female ADHD (M = 33.70 years of age, SD =
8.74), 27 male ADHD+LD (M = 33.96 years of age, SD =
9.89), and 27 female ADHD+LD (M = 33.96 years of age,
SD = 7.99) participants.
1991). The instrument yields linear T-scores on all full
scales and subscales (M = 50, SD = 10). A score of 70T
represents a pronounced deviation from typical responses
of normal community respondents and is considered clinically significant (Morey, 1996). Standardization of the
scale was based on a normative sample including the
general population (n = 1,000), a student population (n =
1,051) and a clinical population (n = 1,246; Morey,
1991). Among the combined normative sample, the internal consistency reliability of the PAI ranged from .81 to
.86, test-retest reliability ranged from r = .79 to r = .92,
and good convergent and discriminant validity has been
demonstrated (Morey, 1991). The PAI has a low reading
level, the average being Grade 4, which is beneficial when
testing participants with ADHD and LD. For the purpose
of this study, three scales were chosen for examination:
Anxiety, comprising cognitive, affective, and physiological subscales; Depression, comprising cognitive, affective,
and physiological subscales; and Aggression, comprising
verbal, physical, and attitude subscales.
Procedure
A clinical facility undertaking assessment of adults
with ADHD in Melbourne, Australia, was approached
regarding collaborative research. The clinic agreed to
make available the assessment results from all adult
clients with ADHD who had been assessed during the
preceding 3 years. All clients had been assessed by registered psychologists as part of a routine admissions procedure. Information obtained from the files included age,
gender, whether a diagnosis of LD was made, the FSIQ,
and subscale scores for anxiety, depression, and aggression as measured by the PAI.
Measures
Cognitive functioning. All participants were assessed
with the WAIS-R or the WAIS-III. The Wide Range
Achievement Test–Revised (WRAT-R; Jastak & Jastak,
1985) was administered to obtain subtest scores for basic
reading, mathematics, and spelling. Consistent with the
diagnostic recommendations of the Diagnostic and
Statistical Manual of Mental Disorders (American
Psychiatric Association, 2000), LD was diagnosed if one
or more of the WRAT-R subtest scores was significantly
lower than predicted from the WAIS-R or WAIS-III FSIQ.
Psychological functioning. The Personality Assessment
Inventory (PAI; Morey, 1991) is a multiscale inventory
that is used to assess various clinical and personality
variables in adults. The inventory is structured, objective,
and nonoverlapping in content; it contains 344 items
each scored on a 4-point Likert-type scale (Morey,
Results
A univariate ANOVA was used to assess differences
between males and females in age and FSIQ, to determine the need for covariates in a factorial betweensubjects MANOVA (2 × 2 MANOVA). There were no
mean group differences indicating that age and FSIQ
would not be included as covariates. Table 1 presents the
means, standard deviations, interaction, and main effects
of the psychological symptoms by group.
Chi-square test for goodness of fit and chi-square test
for independence or relatedness were used to analyze the
global and gender differences in the frequency of
ADHD-only or ADHD+LD diagnoses. Significantly
more of the sample were diagnosed with ADHD+LD
(n = 54) than ADHD only (n = 26), χ2 (1, n = 80) = 9.8,
p = .00. There were no differences in diagnoses (ADHD
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528
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62.60
11.88
69.80
8.75
67.30
11.72
57.10a
12.84
67.60
18.20
64.60
12.59
56.50
7.63
59.40
12.70
58.60
9.81
65.94
18.26
66.06
16.97
69.81a
16.59
70.94
19.81
57.75
13.34
58.06
13.47
52.75
12.22
58.81
12.10
Female
n = 10
61.94
13.49
ADHD
Note: A score of >70T is clinically significant (Morey, 1996).
a. Means significantly differ at p < .05.
*p < .05.
Cognitive anxiety
M
SD
Affective anxiety
M
SD
Physiological anxiety
M
SD
Cognitive depression
M
SD
Affective depression
M
SD
Physiological depression
M
SD
Aggressive attitude
M
SD
Verbal aggression
M
SD
Physical aggression
M
SD
Male
n = 16
61.56
16.68
57.37
11.02
55.48
13.98
56.04
12.38
65.70
15.01
66.04a
12.14
60.44
11.28
61.81
11.34
61.89
11.22
57.70
14.42
53.85
12.30
58.26
13.86
59.87
10.71
69.85
12.71
73.11a
13.89
65.15
14.76
67.30
16.00
67.19
16.44
Female
n = 27
ADHD + LD
Male
n = 27
0.29
3.08
0.45
0.28
0.95
8.70
0.27
0.05
0.48
F(1, 76)
.59
.08
.50
.60
.33
.00*
.61
.82
.49
p
Interaction Effects
0.29
0.29
0.04
3.26
0.01
0.71
0.78
1.80
0.80
F(1, 76)
Gender
.59
.59
.85
.08
.92
.40
.38
.19
.38
p
Diagnosis
0.02
0.03
0.02
1.24
0.15
3.33
1.34
0.90
0.46
F(1, 76)
Main Effects
Table 1
Mean and Standard Deviation Scores of Personality Assessment Inventory Subscales by Group
.89
.87
.90
.30
.70
.07
.25
.35
.50
p
McGillivray, Baker / ADHD and Learning Disabilities 529
only: males n = 16; females n = 10; and ADHD+LD:
males n = 27; females n = 27) on the basis of gender,
χ2 (1, n = 80) = .94, p = .33.
A 2 × 2 MANOVA was performed on nine dependant
variables: cognitive, affective, and physiological anxiety
symptoms; cognitive, affective, and physiological
depression symptoms; and attitude, verbal, and physical
aggression symptoms. The independent variables were
gender (male or female) and diagnosis (with LD or without LD). The multivariate tests were analyzed for significant interaction and main effects using Pillai’s Trace
criterion, which is robust to violations of assumptions
(Coakes & Steed, 1999).
There was a significant multivariate interaction effect
of gender and diagnosis, F(9, 68) = 2.56, p = .01, partial
η2 = .25. Substantial strength of association was indicated between the gender and diagnosis interaction and
the dependant variables (Tabachnick & Fidell, 1996).
The observed power of 91% indicated that it was highly
probable that a true effect did exist (Gravetter &
Wallnau, 1996). The significant multivariate effect for
gender and diagnosis indicates further analysis of univariate effects.
There were no significant main effects for diagnosis,
F(1, 76) = 1.86, p = .07, or for gender, F(1, 76) = 1.39,
p = .20. There was thus no overall difference between
males and females or between individuals with
ADHD+LD and ADHD only with respect to anxiety,
depression, and aggression subscale scores.
However, a significant univariate interaction effect was
found on the cognitive depression symptom variable, F(1,
76) = 8.7, p = .00, partial η2 = .103. Modest strength of
association was indicated between gender and diagnosis
interaction and the cognitive depression symptom variable
(Tabachnick & Fidell, 1996). An observed power of 83% is
evidence that the test was effective in determining differences between variables (Gravetter & Wallnau, 1996).
Examination of the means revealed that females with
ADHD+LD displayed significantly higher levels of cognitive depressive symptoms than females and males with
ADHD only and males with ADHD+LD.
Discussion
This study examined comorbidity in a clinical sample
of adults with ADHD. The primary aim was to determine
whether individuals with ADHD+LD presented with
higher levels of psychopathology than those with ADHD
only, and whether gender impacted symptom presentation.
The finding that significantly more adults were diagnosed
with comorbid ADHD+LD than ADHD only confirms
that the likelihood of an additional diagnosis of LD is
commonplace and comparable to that reported in child
and adolescent populations (e.g., Javorsky, 1996;
Livingston et al., 1990; Mayes et al., 2000; Newcorn
et al., 2001; Rucklidge & Tannock, 2001). Of course, this
may be a feature associated with clinical samples in general, or with this particular clinical sample. However, if
there are differences between these groups in terms of
their risk for psychopathology, or the type of interventions they require, it remains important that comprehensive assessments are undertaken at initial presentation.
The absence of gender differences in the diagnosis of
ADHD only and ADHD+LD was contrary to the reported
predominance of both types in boys (e.g., American
Psychiatric Association, 2000; Javorsky, 1996; Livingstone
et al., 1990) and confirms the findings of Biederman
(2004) that diagnostic rates in adults are equally divided
among men and women. Because there is no evidence that
boys outgrow ADHD to a greater degree than girls (Weiss
& Weiss, 2004), the increase in gender balance with age is
likely to reflect a referral discrepancy. In contrast to
children, adults with ADHD are commonly identified
through self-referral and less frequently on the basis of
hyperactivity and impulsivity symptoms.
Previous research has indicated that children and adolescents with ADHD+LD are at greater risk for anxiety
and depression (Javorsky, 1996; Livingston et al., 1990)
and display more aggressive and disruptive behaviors
than those with ADHD only (Cadesky, Mota, &
Schachar, 2000; McGee, Williams, & Silva, 1988;
Pisecco et al., 2001). However, the assumption that
adults with ADHD+LD would similarly have higher anxiety, depression, and aggression subscale scores than
adults with ADHD only was not supported in this clinical sample. Perhaps the disorders ADHD only and
ADHD+LD might affect the psychological functioning
of adults differently to that reported in children and adolescents. It is also possible that individuals presenting to
a clinic for assessment and intervention are biased
toward psychopathology, limiting the distinction
between the two groups.
Although there was also an overall absence of gender
difference in anxiety, depression, and aggression subscale scores, females with ADHD+LD scored significantly higher on cognitive symptoms of depression than
males with ADHD+LD, and than males and females with
ADHD only. A mean score of 73 is considered clinically
significant (Morey, 1996). A combination of ADHD+LD
appeared to place females at an increased risk of displaying cognitive symptoms of depression, such as
thoughts of worthlessness, hopelessness, and personal
failure. This is in contrast to Livingston et al.’s (1990)
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530 Journal of Attention Disorders
report that girls with ADHD+LD were proportionately
less likely to receive a diagnosis of anxiety or depression
than their male counterparts. Perhaps in females, depression symptoms are more likely to present in association
with maturity.
This study has several limitations. First, the data were
gathered from a clinical sample and thus findings may
not generalize to other populations. Furthermore, the
sample size was relatively small, limiting the statistical
power for examining the association between groups. It
is also important to note that the design lacked a systematic approach to controlling for comorbidity of other psychiatric, cognitive, or behavioral disorders such as ODD,
CD, and anxiety-related and mood disorders, possibly
leading to confounded results. Furthermore, it was
uncertain whether participants had undergone treatment
for additional psychological complaints prior to their
ADHD diagnosis.
An additional limitation relates to the diagnosis of LD
in the ADHD population. It has been long recognized that
LD individuals have problems with written expression,
including poor paragraph structure, spelling, handwriting,
grammar, and punctuation within sentences (White,
1992). Although the WRAT-R tests for basic reading such
as decoding of single words, it does not assess composition, written expression, or reading comprehension
(Jastak & Jastak, 1985). Thus, individuals with writing
disorders, but not disorders relating to reading or mathematics, could have been incorrectly identified as ADHDonly. Tests such as the Wechsler Individual Achievement
Test (WIAT) that include a written expression subtest
could be useful in deriving a more conclusive diagnosis
of LD (Psychological Corporation, 1992).
In summary, despite the caveats mentioned, it was
apparent from this study that a comorbid diagnosis of LD
is common in adults with ADHD. Females and males were
equally affected by ADHD only and ADHD+LD, and there
were no overall gender differences on measures of anxiety,
depression, and aggression. The exception was the cognitive depression subscale of the PAI, with females with
ADHD+LD achieving elevated scores in comparison to
males with ADHD+LD and both males and females with
ADHD only. The level of comorbidity across groups suggests a need for routine assessment of psychopathology in
all individuals with ADHD. This would enable the provision of appropriate treatment to those individuals experiencing additional difficulties. Females with ADHD, most
particularly, may benefit from treatment focused on cognitive components of depression.
There is clearly a need for more research into the risks
of psychopathology in adults with ADHD, and particularly into whether gender or presence of LD impacts risk.
Large-scale studies are needed to explore distinguishing
features of ADHD only and ADHD+LD in clinical and
epidemiological populations, and longitudinal prospective studies may also be useful to ascertain changes in
functioning from childhood through to adulthood.
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J. A. McGillivray, PhD, is associate professor in the School
of Psychology, Faculty of Health, Medicine, Nursing and
Behavioural Sciences at Deakin University, Melbourne,
Australia. She coordinates the Doctor of Health Psychology
program and is an active researcher and supervisor across clinical and health psychology domains.
K. L. Baker is a graduate student from the School of
Psychology at Deakin University, Melbourne, Australia, who
worked on this project under the supervision of Dr.
McGillivray.
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