Understanding Gender Differences in Adult ADHD

55 Pages·2017·0.41 MB·English

University of Colorado, Boulder
CU Scholar
Undergraduate Honors Theses Honors Program
Spring 2018
Understanding Gender Differences in Adult
ADHD
Julia Squeri
[email protected]
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Running head: UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 1

Understanding Gender Differences in Adult ADHD:
Prevalence, Diagnosis, and Associated Impairment.
Julia Squeri
University of Colorado at Boulder

Defense Date: April 4th, 2018
Thesis Advisor: Dr. Erik Willcutt, Psychology and Neuroscience
Committee Member: Dr. Mark Whisman, Psychology and Neuroscience
Committee Member: Michele Simpson, Farrand Residential Academic Program
Key Words: ADHD, Gender, Prevalence, Services, Impairment
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 2

Abstract
The legitimacy and acceptance of adult attention deficit/hyperactivity disorder (ADHD) as a
valid diagnosis is a relatively new development in the field of ADHD research. Research
surrounding the prevalence, diagnosis, manifestation, and associated impairments of adult
ADHD has not been conducted to the extent of the research existing on childhood ADHD, and
few studies have examined the nature of gender differences in adult ADHD. The current study
obtained parent and self-report ratings of ADHD symptoms for an unselected sample of college
students to test competing hypotheses regarding gender differences in the prevalence of adult
ADHD and associated access to clinical services. This study also assessed the impairments
caused by ADHD symptoms in a variety of domains by administering an extensive battery of
impairment measures. The results of this study showed that the gender prevalence difference
differed depending on the rater. Most importantly, our results provide compelling evidence that
adult ADHD is not a benign condition and results in significant impairment across a variety of
domains pertaining to academic, occupational, and other important domains of life functioning.
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 3

Introduction
Background: ADHD
Definition.
Attention deficit/hyperactivity disorder (ADHD) is a neurodevelopmental disorder
defined by impairing levels of inattention, disorganization, and/or hyperactivity and impulsivity
(American Psychiatric Association, 2013). Symptoms of ADHD begin in childhood and often
persist into adulthood, resulting in impairments in social, academic, and occupational
functioning. ADHD symptoms often overlap with those of other externalizing disorders, and it is
often co-morbid with conduct disorders, learning disorders, anxiety disorders, Tourette’s
syndrome (and other tic disorders), and bipolar/mood disorders (Jensen, Martin, & Cantwell,
1997).
Prevalence.
The 5th edition of the DSM estimates a worldwide prevalence of 5% of children and 2.5%
of adults (APA, 2013). Willcutt (2012) also found a prevalence of 5% in children. However,
Willcutt (2012) and Barkley, Murphy, and Fischer (2008) found estimates of 5% in the adult
population. Further, Kessler et al. (2006) estimates that this prevalence rate in adults may be
conservative; from a research methods perspective, the reliance on self-report as well as debate
over the appropriateness of DSM criteria for identifying ADHD in adults could result in an
underestimate. Further research is needed to determine the actual rate of ADHD occurrence in
adults.
Subtypes.
Although the fifth edition of DSM (DSM-V) was released in 2013, DSM-IV and DSM-V
criteria for ADHD are very similar, and nearly all research studies to date are based on DSM-IV
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 4

criteria (including the current project). Therefore, for the remainder of this thesis we focus on
DSM-IV criteria for ADHD.
The DSM-IV defines three nominal subtypes of ADHD (APA, 1994; APA, 2000). These
subtypes are based on differential elevations in two symptom domains; symptoms of inattention
and symptoms of hyperactivity-impulsivity. As described by DSM-IV criteria, the inattention
domain pertains to symptoms of the disorder such as failure to pay attention to detail, difficulty
sustaining attention and remaining focused, problems with organization, and being easily
distracted by extraneous stimuli. The hyperactivity-impulsivity domain refers to symptoms of
more externalizing behaviors, such as fidgeting, inability to sit still, restlessness, excessive
talking/interrupting others, and acting as if “driven by a motor”. The predominately inattentive
type (ADHD-I) refers to individuals with dysfunctional levels of inattention, but not
hyperactivity-impulsivity. Predominately hyperactive-impulsive type (ADHD-H) is
dysfunctional levels of hyperactivity-impulsivity but not inattention; and the combined type
(ADHD-C) describes individuals who present a significant level of symptoms in both domains.
ADHD-I is both the most common subtype in general population estimates and specifically in
adult populations (Willcutt, 2012). ADHD-H is the least common subtype and is found
disproportionately in younger children.
Adult ADHD
Historical context.
Compared to the extensive body of research that exists on childhood ADHD, adult
ADHD has only recently become a focus of widespread clinical attention (Kessler et al., 2006).
As Williamson and Johnston (2015) observed, with regards to adult ADHD “…research in the
area remains relatively new and a comprehensive and coherent picture of the defining
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 5

characteristics of ADHD in adulthood is only beginning to emerge”. The publication of the
DSM-IV in 1994 introduced adult ADHD as a valid diagnosis (APA, 2000). However, the
diagnostic criteria did not change and criteria were developed primarily on and for children,
raising questions over the appropriateness of the criteria for diagnosing ADHD in adults
(Barkley et al., 2008; Kessler et al., 2006). Additionally, the DSM-IV still included an age-of
onset criteria, specifying that some hyperactive-impulsive or inattentive symptoms that result in
impairment must have been present before age seven (APA, 2000). Studies testing the validity of
the DSM-IV age of onset criterion suggest that it represents a somewhat arbitrary threshold that
lacks empirical support (Willcutt, 2012) and "imposes severe limitations on the use of this
criterion with adults” (Barkley et al., 2008). Based on these results the 5th edition of the DSM
(DSM-V) removed this feature; while still defining ADHD as beginning in childhood, an earlier
age of onset is not specified because of the difficulties in establishing a precise age of childhood
onset retrospectively (APA, 2013).
Adult ADHD and impairment.
ADHD is associated with impairment in a variety of major life activities. The DSM-IV
criterion for impairment specifies that ADHD symptoms must lead to clinically significant
impairment in social, academic, or occupational functioning (APA, 2000). The association
between ADHD and functional impairment in childhood has been well established, but far less
research has examined impairment in adult ADHD. Barkley et al. (2008) reported that adults
with ADHD frequently report difficulties in a variety of impairment domains, including
workplace behavior, occupational function, educational settings, social functioning,
dating/relationships, problems managing money, driving, maintaining their health, and more.
Barkley et al. (2008) distinguishes the symptoms of ADHD from their associated impairments by
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 6

defining symptoms as the actions of an individual (cognition/behavior), and impairments as the
consequences of those actions (outcomes/social costs). The domains of impairment specified in
the DSM-IV that must be met for a diagnosis are restricted to those of home, school, and work,
which fails to encapsulate the full array of domains where adults must be able to function
effectively (Barkley et al., 2008).
ADHD and Gender
Why is gender an important consideration?
Independent of ADHD, gender has important implications in virtually every area of life.
Countless social scientists have long noted the role gender has in influencing and structuring
individual behavior, attitudes, and schemas (Ridgeway & Correll, 2004; Valian, 2005; West &
Zimmerman, 1987). Furthermore, gender often has a powerful impact on access to resources and
opportunities (Bobbitt-Zeher, 2011; Jacobs, 1996; Read & Gorman, 2010). Gender differences
have been a long standing and well documented issue in mental health. Underrepresentation of
women in clinical trials and other studies, potential biases in diagnostic criteria or procedures,
potential differences in treatment, and differential access to resources represent a few areas
where women are often disproportionately disadvantaged (Hartung & Widiger, 1998; Read &
Gorman, 2010; Schmucker & Vesell, 1993).
Widespread societal stereotypes about the relation between gender and specific aspects of
mental health may affect both genders negatively. For example, a study by Striegel-Moore et al.
(2009) looking at gender differences in the prevalence of eating disorders found that while few
studies of eating disorders include men, there was still a significant group of men who reported
eating disorder symptoms. In the same way that eating disorders have been largely assumed to
occur mainly in females, ADHD has been stereotyped as a disorder primarily occurring in males.
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 7

Understanding the relationship between ADHD and gender in adulthood is critical to develop a
full understanding of the disorder.
When considering the broad implications of gender in everyday life, it underscores the
importance of understanding the relationship between gender and symptoms of mental disorders
such as ADHD. The stereotype threat has been well documented in studies on ethnicity and race,
starting with Steele and Aronson’s (1995) essays on racial vulnerability. When an individual
belongs to a group for which a negative stereotype exists, and the individual is in a situation that
the negative stereotype pertains to, the anxiety that arises in these situations can result in
impaired performance on a task. Given this, it is plausible that females with ADHD are
susceptible to a ‘double stereotype threat’, thus causing them greater stigmatization and
impairment (Williamson & Johnston, 2015). Negative stereotypes about female’s competence in
a variety of domains combined with the stereotypes of academic impairment and overall
impaired functionality in ADHD could make females with ADHD even more vulnerable to the
stereotype threat than perhaps males with ADHD, and/or males/females without ADHD (Fedele
et al., 2012; Williamson & Johnston, 2015).
Given the pervasive role gender plays in almost every area of society, it is necessary to
understand the relationship between gender and ADHD to have a comprehensive and complete
understanding of the disorder as well as the implications of ADHD in a variety of life domains.
Further, it is necessary to understand adult ADHD in males and females to ensure the best
treatment in clinical practice.
Unexplained ADHD prevalence difference in males and females.
Differential gender prevalence. Currently, there appears to be a higher prevalence of
ADHD in males compared to females, but these prevalence rates vary across studies and settings.
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 8

Male (M) to female (F) ratios range from 2:1 to 3:1 in community samples (APA, 2000;
Bauermeister et al., 2007; Willcutt et al., 2012), and in clinic samples of children the M:F ratio is
often as high as 10:1 (Biederman et al., 2002). In contrast, prevalence studies of adults suggest
that M:F ratios for ADHD range from 1:1 to approximately 2:1 regardless of setting (Willcutt et
al., 2012; Williamson & Johnston, 2015).
The etiology of the higher prevalence in males than females has yet to be determined
(Willcutt, 2012). Further research must be conducted to determine whether this prevalence
difference reflects a true gender difference in risk for ADHD, or if it is potentially an artifact of
methodological or sampling errors. For example, it remains uncertain whether more males than
females have ADHD or if males are simply diagnosed with ADHD at higher rates. In addition,
further research is needed to examine why the prevalence difference in ADHD is smaller in adult
populations than in children. In the remainder of this section we describe two broad categories of
explanations for the gender difference in the prevalence of ADHD in general, as well as for the
observed narrowing of the gender gap.
Potential explanations for a gender difference in the prevalence of ADHD.
Bias hypotheses. Before attempting to identify the etiology of the difference in
prevalence between males and females, it is critical to first test whether there is truly a difference
in the population. Bias hypotheses propose that the methods used for identifying individuals with
a psychological disorder are biased towards the identification and/or treatment of one gender
(Hartung & Widiger, 1998). This would suggest that the traditional methods used to assess and
diagnose ADHD are biased towards the identification of males, resulting in an under
identification of females or over identification of males.
UNDERSTANDING GENDER DIFFERENCES IN ADULT ADHD 9

Clinic referral bias. In its most extreme form, the clinic referral bias hypothesis suggests
that there is no gender difference in the prevalence of ADHD in the population, but males with
ADHD are more likely to be referred for clinical services than are females with ADHD.
Differences in the M:F ratio of ADHD in population based studies (3:1) differs significantly
from that seen in clinical samples, which range between 5:1-9:1 (APA, 2000; Bruchmüller,
Margraf, & Schneider, 2011; Gaub & Carlson, 1997). This suggests that more males than
females are referred to services for ADHD (Bruchmüller et al., 2011), but that the clinic referral
bias is not the full explanation for the gender prevalence difference, as we do see a smaller
population difference that clinic referral does not explain. Nonetheless, the higher percentage of
males with ADHD in clinic settings underscores the need to understand the gender differences in
the prevalence of ADHD as it occurs in the population and in clinical samples. In this study, we
had the unique and important opportunity to test this theory with an unselected undergraduate
sample that should not be influenced by clinical referral bias. Further, because we assessed how
many participants had received clinical services for ADHD, we had the unique opportunity to
test how many individuals who meet symptom criteria for ADHD were then referred for clinical
services. If males in our sample received clinical services at a higher rate than females, this
would support the clinic referral bias as at least part of the explanation for the higher prevalence
of ADHD in males in clinic samples.
Rater bias. The rater bias hypothesis suggests that males and females will be rated
differently even when they exhibit the same behaviors (Hartung & Widiger, 1998). Childhood
ADHD diagnoses are typically made based on symptom ratings by parents and/or teachers, but
inter-rater reliability between teacher, parent, and self-reports of ADHD symptoms has been
shown to be consistently low to moderate (Willcutt, 2012). One potential reason for this low