1
Word count:
Abstract: 189
Text: 6485
Tables: 5
Figures: 0
Supplementary Tables: 1
The Structure of Adult ADHD
Running head: Structure of Adult ADHD
Lenard A. Adler
1*
, Stephen V. Faraone
2
, Thomas J. Spencer
3
, Patricia Berglund
4
, Samuel
Alperin
1,5
, and Ronald C. Kessler
6
July, 2016
Revised November, 2016
1
Department of Psychiatry and Child and Adolescent Psychiatry, New York University Langone
School of Medicine and Psychiatry Service, New York, NY, USA
2
Departments of Psychiatry and of Neuroscience and Physiology, SUNY Upstate Medical
University, Syracuse, NY, USA
3
Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School,
Boston, MA, USA
4
Institute for Social Research, University of Michigan, Ann Arbor, MI, USA
5
Hofstra Northwell School of Medicine, Hofstra University, Hempstead, NY, USA
6
Department of Health Care Policy, Harvard Medical School, Boston, MA, USA
*Corresponding author: Lenard A. Adler, MD, Department of Psychiatry and Child and
Adolescent Psychiatry, New York University Langone School of Medicine and Psychiatry
Service, New York City, USA; Tel. (312) 753-7537; Fax (312) 753-7886;
Lenard.adler@nyumc.org.
This article is protected by copyright. All rights reserved.
This is the author manuscript accepted for publication and has undergone full peer review but
has not been through the copyediting, typesetting, pagination and proofreading process, which
may lead to differences between this version and the Version of Record. Please cite this article
as doi: 10.1002/mpr.1555
2
ABSTRACT
Although DSM-5 stipulates that symptoms of attention-deficit/hyperactivity disorder (ADHD)
are the same for adults as children, clinical observations suggest that adults have more diverse
deficits than children in higher-level executive functioning and emotional control. Previous
psychometric analyses to evaluate these observations have been limited in ways addressed in the
current study, which analyzes the structure of an expanded set of adult ADHD symptoms in 3
pooled U.S. samples: a national household sample, a sample of health plan members, and a
sample of adults referred for evaluation at an adult ADHD clinic. Exploratory factor analysis
found 4 factors representing executive dysfunction/inattention (including, but not limited to, all
the DSM-5 inattentive symptoms, with non-DSM symptoms having factor loadings comparable
to those of DSM symptoms), hyperactivity, impulsivity, and emotional dyscontrol. Empirically-
derived multivariate symptom profiles were broadly consistent with the DSM-5 inattentive-only,
hyperactive/impulsive-only, and combined presentations, but with inattention including
executive dysfunction/inattention and hyperactivity-only limited to hyperactivity without high
symptoms of impulsivity. These results show that executive dysfunction is as central as DSM-5
symptoms to adult ADHD, while emotional dyscontrol is more distinct but prominent resent in
the combined presentation of adult ADHD.
Key Words: adults; ADHD; attention-deficit hyperactivity disorder; epidemiology
This article is protected by copyright. All rights reserved.
3
Adult Attention Deficit Hyperactivity Disorder (ADHD) is a commonly-occurring childhood-
onset disorder that often persists into adulthood (Kessler et al., 2006). Although DSM-5 requires
fewer symptoms among adults than children (American Psychiatric Association., 2013), the
symptoms are stipulated to be the same for adults as children despite the fact that clinical
observations suggest that the frank hyperactivity of childhood ADHD manifests more as a sense
of internal restlessness among adults (Adler and Cohen, 2004) and that adults have a more
diverse set of deficits than children in higher-level executive functioning and emotional control
(Barkley et al., 2008; Faraone et al., 2010; Surman et al., 2011; Ward et al., 1993).
A number of researchers have attempted to confirm these clinical observations by
developing expanded assessments that include deficits in executive functioning and in emotional
control along with the DSM symptoms of inattention (AD) and hyperactivity-impulsivity (HD)
and carrying out exploratory factor analyses of this expanded symptom set among patients with
ADHD and controls (Amador-Campos et al., 2014; Christiansen et al., 2011; Conners et al.,
1999; Kessler et al., 2010; Marchant et al., 2013; Marchant et al., 2015). These studies have
found a 2-factor structure in studies of the clinician-administered Wender-Reimherr Adult
Attention Deficit Disorder Scale (WRAADDS) (Marchant et al., 2013) and the self-report
version of that scale (Marchant et al., 2015) compared to 3-factor (Kessler et al., 2010), 4-factor
(Amador-Campos et al., 2014; Conners et al., 1999), or 6-factor (Christiansen et al., 2011)
solutions in studies using other instruments.
This article is protected by copyright. All rights reserved.
4
In evaluating these discrepant results, it is important to note that published WRAADDS
factor analyses were carried out on 7 rationally-constructed subscales rather than on the more
than 60 underlying symptoms assessed in the WRAADDS. The 2-factor solutions showed the
inattention and disorganization subscales loading on the first factor, 3 emotion subscales (temper,
affective liability, emotional over-reactivity) loading on the second factor, and the remaining
subscales of hyperactivity/restless and impulsivity loading on both factors. However, the items in
the overall scale were combined into these 7 presumed underlying subscales based on theory
rather than on empirical considerations. To our knowledge, no empirical data have ever been
reported confirming the empirical validity of these 7 subscales. Critically, the resulting 7x7
correlation matrix among the rational WRAADDS subscales contains only 21 correlations (i.e.,
7x6/2 = 21), making it impossible to identify a factor model with more than 2 correlated factors,
as a 3-factor model would contain 21 factor loadings (7 for each of 3 factors) and 3 correlations
among factors, which would exceed the number of degrees of freedom in the correlation matrix.
As a consequence, the “finding” of a 2-factor structure in the WRAADDS exploratory factor
analyses is actually a construction rather than a finding.
This problem could have been avoided by carrying out the WRAADDS factor analyses
on the symptom-level data rather than introducing the intermediate step of creating rationally-
constructed subscales, but this was not done in the WRAADDS studies because the samples on
which the factor analyses were based were thought to be too small to allow symptom-level factor
analyses to be carried out. For example, the paper reporting the factor structure of the self-report
This article is protected by copyright. All rights reserved.
5
version of the WRAADDS was based on a mere 120 community controls and 122 patients with
adult ADHD (Marchant et al., 2015). But were these samples too small? Guidelines on the
required sample size for exploratory factor analysis have been inconsistent (Comrey and Lee,
1992; Gorsuch, 1983; Kline, 1994), but recent simulations show that the sample size required to
recover a stable factor structure is a joint function of number of factors, number of items per
factor (with the required sample size stabilizing after 6-10 items per factor), and strength of
factor loadings (MacCallum et al., 1999; Mundfrom et al., 2005). In addition, sample size
requirements are higher when the symptoms are dichotomies, as they typically are in factor
analyses of psychiatric symptoms, and when symptom prevalence is variable (Pearson and
Mundfrom, 2010). Based on these results, a scale like the WRAADDS, where the number of
items per hypothesized factor is 8-9, and there might be as many as 7 factors, the minimum
required sample size for good recovery of the population factor structure would be 1,600-2,000.
For a 4-factor solution of the sort hypothesized to exist by many experts in ADHD (i.e.,
inattention/executive dysfunction, hyperactivity, impulsivity, emotional dyscontrol), a stable
factor structure based on scales with between 9 (the number of DSM-5 symptoms of inattention
and the number for hyperactivity/impulsivity) and 12 items the minimum required sample size
would be 320-500 respondents (Pearson and Mundfrom, 2010). Even the smallest of these
required sample sizes is several times larger than the sample size used in the factor analysis of
the self-report version of the WRAADDS. However, the sample size used in an earlier factor
analysis of the clinician-administered version of the WRAADDS that combined data across 3
This article is protected by copyright. All rights reserved.