Measuring adult Attention Deficit Hyperactivity Disorder using the Quantified Behavior Test Plus

Abstract

Attention Deficit Hyperactivity Disorder (ADHD) occurs in approximately 5% of the adult population and includes cardinal symptoms of hyperactivity, inattention, and impulsivity that may be difficult to identify with clinical routine methods. Continuous performance tests are objective measures of inattention and impulsivity that, combined with objective measures of motor activity, facilitate identification of ADHD among adults. The aim of the present study was to examine the sensitivity, specificity, and a composite measure of ADHD using objective measures of the ADHD-cardinal symptoms in adult participants with ADHD and non-ADHD normative participants. Cardinal symptoms were measured in 55 participants having ADHD, 202 non-ADHD normative participants, as well as 84 ADHD normative participants using the Quantified Behavior Test Plus. This test measures inattention and impulsivity using a continuous performance test, and hyperactivity using a motion-tracking system. A predictive variable for the detection of ADHD called Prediction of ADHD yielded 86% sensitivity and 83% specificity. A composite measure of ADHD cardinal symptoms was developed using a Weighed Core Symptoms scale that indicated the total amount of ADHD symptoms on a numeric scale from 0 to 100. The total amount of ADHD symptoms was measured on a scale and predicted with the categorical variable in a majority of the cases in the present study. Further studies are needed in order to confirm the results with regard to additional clinical and normative samples. Careful consideration of potential sex and diagnostic subtype differences are noteworthy aspects for future examinations of the new instruments.

Full text

Measuring adult Attention Deficit Hyperactivity Disorder using the
Quantified Behavior Test Plus
Hanna Edebol,1Lars Helldin,2and Torsten Norlander3,4
1Department of Psychology, Karlstad University, Karlstad, Sweden, 2Department of Psychiatry, The
NU-Health Care, Trollhättan, Sweden, 3Evidens Research and Development Center, Göteborg,
Sweden, 4Division of Psychology, Department of Clinical Neuroscience, Karolinska Institutet, Solna,
Sweden
Abstract: Attention Deficit Hyperactivity Disorder (ADHD) occurs in approximately 5% of the adult population and includes
cardinal symptoms of hyperactivity, inattention, and impulsivity that may be difficult to identify with clinical routine methods. Continuous
performance tests are objective measures of inattention and impulsivity that, combined with objective measures of motor activity, facilitate
identification of ADHD among adults. The aim of the present study was to examine the sensitivity, specificity, and a composite measure of
ADHD using objective measures of the ADHD-cardinal symptoms in adult participants with ADHD and non-ADHD normative partici-
pants. Cardinal symptoms were measured in 55 participants having ADHD, 202 non-ADHD normative participants, as well as 84 ADHD
normative participants using the Quantified Behavior Test Plus. This test measures inattention and impulsivity using a continuous
performance test, and hyperactivity using a motion-tracking system. A predictive variable for the detection of ADHD called Prediction of
ADHD yielded 86% sensitivity and 83% specificity. A composite measure of ADHD cardinal symptoms was developed using a Weighed
Core Symptoms scale that indicated the total amount of ADHD symptoms on a numeric scale from 0 to 100. The total amount of ADHD
symptoms was measured on a scale and predicted with the categorical variable in a majority of the cases in the present study. Further studies
are needed in order to confirm the results with regard to additional clinical and normative samples. Careful consideration of potential sex
and diagnostic subtype differences are noteworthy aspects for future examinations of the new instruments.
Keywords: adults; Attention Deficit Hyperactivity Disorder; psychometrics; objective measures
Correspondence: Ms. Hanna Edebol, Department of Psychology, Karlstad University, Universitetsgatan 2, SE-651 88 Karlstad, Sweden.
Email: hanna.edebol@kau.se
The study has been approved by the Regional Ethical Board in Uppsala.
Received 6 February 2012. Accepted 2 September 2012.
In the 1950s, Continuous Performance Tests (CPT) were
originally used for testing the signal detectability of radar
operators. Development intended for psychiatric care and
research eventually began in human subjects with brain
damage (Rosvold, Mirsky, Sarason, Bransome, & Beck,
1956). From the early stages, neuropsychological perfor-
mance deficits were the targets of much research because of
the association with poor attention and impulse control. CPT
measures were found to correspond with cardinal symptoms
of Attention Deficit Hyperactivity Disorder (ADHD), that is,
hyperactivity, inattention, and impulsivity (American Psychi-
atric Association [APA], 2000).The new measures, however,
were merely considered for child and adolescent populations.
Since then, the CPT paradigm has expanded both in terms of
apparatus and techniques of testing. From merely being
revolving drums on which letters are mounted side by side
(Rosvold et al., 1956), it nowadays typically includes com-
puterized presentation of visual or auditory stimuli at a rapid
pace for a fixed time. The participant is instructed to respond
to some stimuli, that is, targets, and to withhold response
to other stimuli, that is, nontargets. What the CPT paradigm
actually measures is based on clinical assumptions, expert
PsyCh Journal 2(2013): 48–62
DOI: 10.1002/pchj.17
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© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

judgments (Riccio & Reynolds, 2001), and face validity
(Brocki, Tillman, & Bohlin, 2010). Omission errors are
related to inattention and commission errors to impulsivity.
Inattention may be defined as the incapacity to persist during
a task, while impulsivity is the incapacity to inhibit an inap-
propriate response (Kaplan & Stevens, 2002).
Robust findings throughout the years are that children
with ADHD typically identify fewer targets, respond to more
nontargets and demonstrate decreased target detection with
time (Charles, Schain, Zelniiker, & Guthrie, 1979; Corkum
& Siegel, 1993; Douglas, 1972; Grodzinsky & Barkley,
1999; Losier, McGrath, & Klein, 1996; Pliszka, 1992;
Riccio & Reynolds, 2001; Sykes, Douglas, & Morgenstern,
1973). Accumulated research demonstrates discriminative
power forADHD versus nonaffected controls, but the results
are more inconsistent for ADHD versus other psychia-
tric disorders (McGee, Clark, & Symons, 2000; Riccio &
Reynolds, 2001).
The paradigm has been developed with prime reference
to children with ADHD, but is also administered frequently
to adults with the disorder. As a result, a lack of sensitivity
and ceiling effects have been documented when applying
child norms to adult populations, particularly in cases with
less severe symptomatology (Corbett & Stanzcak, 1999;
Seidman, Biederman, Faraone, Weber, & Ouellette, 1997).
When standardizing CPTs for adults, however, groups with
ADHD have most often been identified as impaired com-
pared with healthy controls. Recent meta-analytic reviews
(Boonstra, Oosterlaan, Sergeant, & Buitelaar, 2005; Frazier,
Demaree, & Youngstorm, 2004; Hervey, Epstein, & Curry,
2004) have reported medium to high effect sizes (Cohen’s d)
for many of the parameters of inattention and impulsivity.
A meta-analytic review of neuropsychological measures
(Schoechlin & Engel, 2005) found significant (pⱕ.01)
pooled effect sizes for sustained attention (-0.52) on various
CPTs, which placed them among the top discriminating
measures of adult ADHD versus healthy controls.
Even though the CPTs have advanced in the past 60 years,
they do not facilitate measures of hyperactivity. Instead,
single- and multiple-channel actometry and motion-tracking
systems have been used for recording motor activity in chil-
dren and adults with the disorder. Children with ADHD
demonstrate more frequent head-shifts, covering longer
distances and greater areas, and with a more linear but less
complex movement pattern in comparison to controls
(Teicher, Ito, Glod, & Barber, 1996). Two studies (Boonstra
et al., 2007; Tuisku et al., 2003) that used actometry in adults
with ADHD or with ADHD and antisocial personality dis-
order reported higher frequencies of movements inADHD as
compared to nonaffected controls. The need for the activity
domain to be objectively accessible and measurable in adult
ADHD patients has been critically discussed, with reference
to reduced levels of motor activity with increased age
(Brocki et al., 2010) and the influence of diagnostic sub-
types. However, the clinical definition of ADHD (APA,
2000) stipulates age-relevant symptoms of hyperactivity for
diagnosis. Many adult persons with ADHD report fidgeting
their feet and fingers (74%) and having problems remain-
ing seated (66%) several times a day (Barkley, Murphy, &
Kwasnik, 1996). Symptoms of inattention hold low specific-
ity for ADHD and most studies with clinical controls report
low discriminative power for conventional CPT measures.
Hyperactivity is a distinct cardinal symptom of ADHD that
is possible to measure in adulthood (Boonstra et al., 2007;
Polcari, Fourligas, Navalta, & Teicher, 2010; Tuisku et al.,
2003), and it may improve the ability to separate ADHD
from psychiatric disorders with inattentive and impulsive
symptom overlap.
Lis et al. (2010) were the first to investigate motor activity
in adult persons with ADHD (N=20) and compare them
with healthy and matched controls (N=20) using the Quan-
tified Behavior Test Plus (QbTest-Plus). This test combines a
motion-tracking system (MTS) and a CPT on the computer.
It was developed for the purpose of reducing ceiling effects
and to measure the ADHD core symptoms among adults.
The highest separation of the groups was reported for the
MTS measures that included parameters called microevents
(the number of small motor shifts), time active (amount of
time with motor activity), distance (m), and area (m2). With
regard to the CPT measures, significant group differences
were found for omission errors only. Motor activity was
associated with increased levels of cognitive impairment in
the ADHD group only. Motor activity in the ADHD group
was up to 3.5-fold higher than that of healthy controls during
the 20 min of standardized testing. The group differences
became more accentuated as the period prolonged. Lis et al.
(2010) suggested that, although observable motor behaviors
might decrease with age, higher motor activity persists
and may be recorded in adults with ADHD. Another study
(Edebol, Helldin, & Norlander, in press) investigated the
ability of the QbTest-Plus to discriminate ADHD from
clinical controls with bipolar II disorder or borderline per-
sonality disorder and from participants who were assessed
for but excluded from a diagnosis of ADHD. Objective
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motor activity measures were the most predictive marker of
ADHD versus other clinical diagnoses, and the study pro-
vided support for composite measures of the disorder. Taken
together, previous studies combining CPT and motor activity
measures suggest an increased diagnostic accuracy and
discriminative power for adult ADHD using combined and
composite measures.
Despite access to simultaneous measurement techniques
for the entire ADHD core symptom spectra, there is a lack of
research regarding composite measures of the disorder. The
present study wished to examine the possibility of combin-
ing measures of hyperactivity, inattention, and impulsivity
from the QbTest-Plus into a composite measure for quanti-
fication of the disorder. The present study also wished to
examine the predictive power of the QbTest-Plus in terms of
its sensitivity and specificity for ADHD and non-ADHD
normative participants. The aims of the present study were
therefore twofold: first, to examine the predictive power of
the QbTest-Plus in terms of its sensitivity and specificity for
adult participants with ADHD and non-ADHD normative
participants; and second, to develop a composite measure for
the entire ADHD core symptom triad on the basis of the
measures provided by the QbTest-Plus.
Methods
Participants
This study consisted of 341 participants, comprising three
groups. The first were participants with ADHD (N=55), the
second were non-ADHD normative (N=202), and the third
were ADHD normative (N=84).
The ADHD group
Demographic data for the ADHD group are presented in
Table 1 and psychiatric data are presented in Table 2. Diag-
nostic assessments adhered to the Diagnostic and Statistical
Manual of Mental Disorders, 4th edition (DSM-IV;APA,
2000). Clinical assessments had previously been carried
out within two separate psychiatric clinics: the NU-Health
Care in Västra Götaland, Sweden (N=24) and the psychiat-
ric division in the County Council of Värmland, Sweden
(N=19). Assessments included similar neuropsychological
tests and procedures at both psychiatric clinics, such as tests
of memory, attention, executive functioning, intelligence,
interviews, observations, and somatic examinations. None
of the participants used stimulants on the day of the
QbTest-Plus, but 34 participants generally used stimulants.
The approximate mean time from taking stimulant medica-
tion at the first minute of the QbTest-Plus was 30.55 hr
(SD =9.36 hr, range =16–55 hr). A total of 22 persons did
not use psychotropic medication, while 33 persons used
one (n=19), two (n=10), three (n=1), four (n=2), or five
(n=1) psychotropic medications. Medications included
antidepressants (n=26), antiepileptics (n=13), anxiolytics
(n=10), neuroleptics (n=7), and anticholinergics (n=1).
The approximate mean time from taking psychotropic
medication at the first minute of the QbTest-Plus was
16.27 hr (SD =15.11 hr). Statistical analyses (independent
samples t-test, 5% level) regarding age, education, Global
Assessment of Functioning (GAF) total (Luborsky, 1962),
GAF symptoms, GAF function, and age at first contact with
psychiatry yielded no significant differences between the
Table 1
Demographic data for the ADHD group (N=55)
Demographic n% M SD
Age 55 33.35 8.84
Gender
Male 25 45.5
Female 30 54.5
Body Mass Index 55 26.18 4.94
Nicotine consumption
No 23 41.8
Yes 32 58.2
Minutes from nicotine consumption
when performing the Quantified
Behavior Test Plus
32 38.19 27.43
Education
Junior high school 12 21.8
Partial high school 15 27.3
Complete high school 19 34.6
Partial graduate school 5 9.1
Complete graduate school 4 7.3
Employment status
Sick leave 18 32.7
Full- or part-time employment 13 23.6
Rehabilitation/practice 7 12.7
Unemployed 6 10.9
Studying 5 9.1
Retired 4 7.3
Parental leave 2 3.6
Income
Public maintenance 38 68.7
Employment 11 20.4
Student loans 4 7.4
Other income 2 3.7
Social status
Married/common-law 21 38.2
Single 23 41.9
Partner 11 20.0
Household
Single 24 43.6
Shared 31 56.4
Note: ADHD =Attention Deficit Hyperactivity Disorder.
50 Objective measures of adult ADHD
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

sexes (ps>.05). For means and standard deviations, see
Tables 1 and 2.
The non-ADHD normative group
The second group of participants (N=202) included 114
men and 88 women whose mean age was 31.06 years
(SD =10.27 years, range =18–53 years). The group was
recruited from the general population in order to represent
non-ADHD normative participants and they did not have
a diagnosis of ADHD. Participants were screened for
symptoms of ADHD using the adult ADHD Self-Report
Scale (ASRS; described in the instruments section). The
mean total for the six items that were most predictive of
ASRS, that is, the screener, was 8.90 (SD =3.53), and the
mean total overall was 24.56 (SD =8.66). An independent
samples t-test confirmed that the ASRS scores of the
screener and the total were significantly different (ps<.001)
from those of the ADHD group presented in Table 2. An
independent samples t-test yielded no significant differences
for men and women in the non-ADHD normative group with
regard to age or ASRS (ps>.05).
The ADHD normative group
The third group of participants (N=84) included 47 men
and 37 women withADHD whose mean age was 35.07 years
(SD =10.36 years). The participants had previously com-
pleted the QbTest-Plus as a part of a thorough neuropsychi-
atric assessment performed at the neuropsychiatric clinic,
Cereb AB, in Stockholm, Sweden. Apart from the QbTest-
Plus, the neuropsychiatric assessment also included tests
of cognitive functioning, attention, intelligence, everyday
functioning, and ADHD symptomatology.
The group was recruited for methodological purposes to
represent an ADHD normative group during the develop-
ment of the variable Prediction of ADHD (PADHD; see
the instruments section) and the Weighed Core Symptoms
scale (WCS; see the instruments section). For the PADHD,
the ADHD normative data were employed to evaluate the
levels of sensitivity and specificity. For the WCS, the ADHD
normative data were employed in the assessment of core
symptom manifestations and to examine the cut-off points
on the scale. As this group was solely a normative reference
group for ADHD in the present study, with the purpose of
examining the PADHD and the WCS, findings from the
group are not reported in the statistical analyses of the results
section.
Design
The present study had a quantitative design. Statistical
analyses of variance and a Fisher’s exact test were conducted
using the software program Statistical Package for the Social
Sciences version 19.0 for Windows (SPSS Inc., 2012). The
independent variables of the present study were Group (non-
ADHD normative group, ADHD-group) and Gender (men,
women). There were 202 participants in the non-ADHD
normative group and 55 participants in the ADHD group.
The total number of men was 139 and the total number of
women was 118. The dependent variables of the present
Table 2
Psychiatric data for the ADHD group (N=55)
Characteristic n% M SD
Age at first contact with psychiatry 55 21.46 9.75
Global assessment of functioning closest
in time to the Quantified Behavior
Test Plus
55 53.89 7.20
Function 55 54.59 8.68
Symptoms 55 54.49 6.86
Psychiatric hospitalization
Never 24 43.6
One time 20 36.4
Several times 11 20.0
Age at first hospitalization 31 24.86 7.80
Age at ADHD diagnosis 55 31.96 9.02
Diagnostic subtype
ADHD-C 43 78.2
ADHD-PI 12 21.8
ADHD behavior rating scales
ASRS total 55 44.58 10.98
ASRS screener 55 15.82 4.25
Wender Utah Rating Scale 25 most
predictive
55 53.85 18.10
Wender Reimherr ADHD Symptoms
Scale for Patients total
55 86.91 21.37
Conner’s Adult ADHD Rating
Scale total
55 47.25 12.14
Current psychiatric comorbidity
None 24 43.6
One 24 43.6
Two 7 12.7
Age at first comorbidity 31 31.96 8.99
Age at second comorbidity 7 29.86 5.81
Distribution of current comorbidity
Substance abuse 7 18.4
Relapsing/moderate depression 7 18.4
Anxiety disorders 8 21.1
Mixed anxiety/depression 2 5.3
Bipolar disorders 6 15.8
Personality disorders 4 10.5
Adjustment disorders 2 5.3
Autism 1 2.6
Dyslexia 1 2.6
Note: ADHD =Attention Deficit Hyperactivity Disorder; ASRS =ADHD Self-
Report Scale.
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study were the core ADHD symptoms of hyperactivity, inat-
tention, and impulsivity, as well as the composite measure,
the WCS scale. The categorical variable, PADHD, was ana-
lyzed using Fisher’s exact test.
The dependent variables were developed statistically from
the core symptom measures from the QbTest-Plus, that is,
hyperactivity measured in distance, inattention measured
using omission errors, and impulsivity measured using com-
mission errors. The Q-score (Qb-test raw score) of each core
symptom was transformed into percentages, where 0% indi-
cated the maximum quantity of the symptom and 100%
indicated the complete absence of the symptom. The addi-
tional scale, WCS, was constructed using weighed Q-scores
from the symptom scales. The WCS runs from 0, which
indicates the maximum amount of ADHD symptoms, and
100, which indicates a complete absence of ADHD symp-
toms. The weighed Q-score principle was based on analyses
of Receiver Operator Curves, in which hyperactivity was the
most predictive item ofADHD and therefore multiplied by 3,
inattention was the second most predictive item and multi-
plied by 2, and impulsivity was ascribed no additional weight
because of its relatively low predictive value.
The categorical variable, PADHD (no ADHD, yes
ADHD), was also based on the raw scores from the measures
of the QbTest-Plus (Q-scores), that is, hyperactivity mea-
sured in distance, inattention measured using omission
errors, and impulsivity measured using commission errors. It
was analyzed in the present study using Fisher’s exact test
(p<.05) with the PADHD (no ADHD, yes ADHD) and
Group (non-ADHD normative group, ADHD group). For
further information on how the PADHD was conducted see
the instruments section.
Instruments
QbTest-plus
This instrument (QbTech AB, 2010a, 2010b) combines a
continuous performance test (CPT), installed as a software
program on a PC, and an activity test performed over a
20-min period. While performing the CPT on the computer,
the movements of the participants were recorded using an
infrared camera following a reflective marker attached to a
headband. The CPT test involves rapid presentations of four
types of stimuli (a red circle, a blue circle, a red square, and
a blue square) and the participants were instructed to press a
handheld button when a stimulus subsequently repeated
itself (a target) and not to press the button each time the
stimulus varied relative to the previous one (a nontarget).
The stimuli were presented at a rate of one per 2 s, with each
one visible for 200 ms, and the total number of stimuli was
600, presented with a 25% target probability. The purpose of
the QbTest-Plus is to provide objective information regard-
ing cardinal symptoms of ADHD: hyperactivity assessed on
the basis of motor activity measured using the camera, and
inattention and impulsivity measured on the basis of the CPT
(QbTech AB, 2010b).
In this study, hyperactivity has been operationalized with
the parameter called “distance,” that is, the length of the path
describing the movement of the headband reflector during
the test. Inattention has been operationalized on the basis of
omission errors, that is, when no response is registered and
the stimulus was a target. Finally, impulsivity has been
operationalized on the basis of commission errors, that is,
when a response was registered and the stimulus was a
nontarget. A former study of the QbTest-Plus (Lis et al.,
2010) demonstrated the relative significance of the core
symptoms, with measures of hyperactivity being the most
and inattention the second-most efficient measure of ADHD,
whereas the level of impulsivity was not significantly higher
in adults with ADHD compared with healthy controls
(p>.05).
In this study, the relative significance of the core symp-
toms was taken into consideration by the means of the WCS,
which weighs the scales of the core symptoms into one
measure. The WCS scale was derived from the ADHD group
and the non-ADHD normative group of the present study,
and was tested on the normative group with ADHD, as
described in the participants section. The ADHD normative
group was employed in the assessment of core symptom
manifestations and to examine the cut-off points on the
scale. The best model adjustment was found when the results
of the core symptoms were summed after the results of
hyperactivity had been multiplied by 3, the results of inat-
tention had been multiplied by 2, and the results
of impulsivity by 1. Then, the total results from the ADHD
group of the present study, the ADHD normative group, as
well as the non-ADHD normative group, were categorized
using 10 cut-off points (visual binning, With =9.09%., i.e.,
each individual could gain one out of eleven sums on the
scale). In the present study, the WCS correlated (Pearson’s r)
with hyperactivity (r=.76, p<.001), inattention (r=.72,
p<.001), and impulsivity (r=.54, p<.001), and those
results were also approximately the same when correlations
were computed only for the ADHD group or only for the
non-ADHD normative group.
52 Objective measures of adult ADHD
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

The categorical variable, PADHD (no ADHD, yes
ADHD), was based on qualitative analyses of raw scores
from the operationalized measures of the QbTest-Plus
(Q-scores). Data were derived from the ADHD group and
the non-ADHD normative group of the present study. The
qualitative analyses included testing the effects of setting
various cut-off points as well as combining and coordinat-
ing cut-off points from the core symptom measures of
hyperactivity (distance), inattention (omission error), and
impulsivity (commission errors). The effects of the cut-off
points were evaluated in terms of sensitivity (positive pre-
dictive value) and specificity (negative predictive value) for
the ADHD group and the non-ADHD normative group.
Multiple cut-off points for each of the three core symptoms
combined with the coordinated cut-off points from the
other two core symptoms resulted in multiple pathways to
either of the two categories of PADHD (no ADHD, yes
ADHD). Except for distance, omission errors, and commis-
sion errors, the other parameters from the QbTest-Plus were
assessed in terms of sensitivity and specificity, but accord-
ing to the aggregated assessment trials, the most efficient
parameters for the identification of ADHD and separation
from non-ADHD normative participants were the three
parameters that were ultimately included in the PADHD.
Apart from the coordinated cut-off points for distance,
omission errors, and commission errors, the PADHD also
included supplementary cut-off points from a parameter
called the normalized variation Q-score (NVQ). This vari-
able is a mathematical measure defined as the standard
deviation of the reaction time divided by the reaction time.
It was included in the PADHD because it improved the
predictive power. The NVQ is not a principal parameter in
the PADHD, but is a supplementary parameter for the three
core symptom measures.
In order to make sure that the PADHD was not simply an
adjustment for the ADHD group and the non-ADHD norma-
tive group of the present study, the PADHD was evaluated in
terms of sensitivity and specificity for the ADHD normative
group described in the participants section of the present
study. The level of sensitivity became somewhat higher for
the ADHD normative group than the ADHD group of the
present study. This gave credit to the PADHD as not being
an adjustment to the ADHD group of the present study. After
the PADHD had been conducted through qualitative analyses
and evaluated on the ADHD normative group described
in the participants section, it was analyzed statistically
for the present study using Fisher’s exact test (p<.05) for
Prediction of ADHD (no ADHD, yes ADHD) and Group
(non-ADHD normative group, ADHD group).
Global Assessment of Functioning Scale
The Global Assessment of Functioning (GAF) Scale (Lubor-
sky, 1962) can be found in the DSM-IV (APA, 2000), and
estimates psychological, social, and occupational function-
ing on a numeric continuum (0–100) of mental health and
illness for adult persons. The first interval (0–50) describes
severe symptoms, whereas the second interval (50–100)
describes functional disabilities. The total score (GAF-total)
of this scale should be the lowest score of either the symp-
toms (GAF-symptom) or the functional disability score
(GAF-function). The GAF-scores presented in the current
study were calculated by licensed clinicians and were the
scores reported in the psychiatric records closest in time to
the QbTest-Plus.
The Adult Self Report Scale for adult ADHD v1.1
The Adult Self-Report Scale (ASRS) is a screening instru-
ment (Kessler et al., 2005; Kessler & Üstün, 2005) that was
developed by the World Health Organization in order to
provide initial information about the prevalence of ADHD
symptoms for both research and health-care centers. It is
derived from the criteria for ADHD in the DSM-IV.PartA
includes the six most predictive items while part B holds an
additional 12 items, all rated on a 5-point scale (0 =never,
1=rarely, 2 =sometimes, 3 =often, and 4 =very often).
Each item has a cut-off point of either 2 (sometimes) or 3
(often), and a result of four or more items listed above the
cut-off point in part A is used as an inclusion/exclusion
criterion for clinical purposes and in research programs, such
as in the normative sample of the Qbtest-Plus (QbTech AB,
2010a). The internal consistency for the patient-administered
version is .88 (Cronbach’s alpha; Kessler et al., 2005).
Procedure
Since 2008, the Department of Psychology at Karlstad Uni-
versity has been participating in a research program regard-
ing the objective markers of adult ADHD. The research
program includes studies on both the diagnostic and treat-
ment aspects of the disorder. It is organized as collabo-
ration between the Department of Psychology at Karlstad
University, Sweden, the Cognitive Neuroscience Centre for
Psychiatry at the University of Giessen, Germany, the psy-
chiatric clinic in the NU-Health Care in Västra Götaland,
Sweden, the psychiatric division of the County Council
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of Värmland, Sweden, and the neuropsychiatric clinic
Cereb AB in Stockholm, Sweden. A presentation of the
process for recruitment and analysis is given in Figure 1.
The study procedures were examined and approved by the
Regional Ethical Review Board of Uppsala, Sweden, in
February 2008.
The ADHD group
Nurses and trained clinicians at the psychiatric centers
screened psychiatric records and recruited participants
via mail and telephone. The vital inclusion criteria for the
ADHD group were an age of 18–65 years, a diagnosis of
ADHD according to the DSM-IV (APA, 2000), a described
chronic course of ADHD symptomatology from childhood
to adulthood with some symptoms present before 7 years of
age and continuing to meet the DSM-IV criteria at the time of
assessment, and an accepted withdrawal from central stimu-
lant treatment 24 hr prior to the QbTest-Plus. Exclusion cri-
teria for this group were any clinically unstable psychiatric
condition including, but not limited to, acute mood disorder,
acute bipolar disorder, and acute obsessive-compulsive
disorder (OCD), and not meeting the diagnostic criteria
for ADHD in the DSM-IV. The study-specific procedures
were explained and information about withholding one’s
diagnostic and medical status from the researcher as well
as withdrawing from central stimulant treatment 24 hr prior
to participation were highlighted in particular. On the
day before participation, the participants received a short
message on their mobile phone that included a reminder of
the day, time, and location of the study.
When arriving at the psychiatric center, the participant
was met by a researcher in the lobby and taken to the test
room, where information about the study procedures was
provided. The written consent form was then introduced,
and a signed copy received from the participant. The ASRS
and a medical form, regarding the paticipant’s medical
status and the last time that central stimulant treatment
was used, were then filled out. The patient’s diagnosis and
status was unknown to the researcher during the whole
process of experimental testing and assessment. Prior to
testing, the participant was seated on a chair without arm-
rests in order to ensure a nonreclining body position and
also provided with the reflective head-band and the hand-
held button.
Instructions on how to do the QbTest-Plus were given first
verbally and then by the means of a standardized video
(QbTech AB, 2010b) that presented the procedures for the
QbTest-Plus. The participant performed a 1-min pretest to
make sure the instructions had been understood correctly.
After this, the participant performed the QbTest-plus for
20 min. A room with minimal visual and auditory stimuli
was used for testing. After testing, the participant answered
demographic and other relevant questions regarding his or
her psychiatric history, but no questions that endangered
the blind design were asked. For the purposes of analysis,
data covering the results and methods used for clinical
LiV
n =19
CNC
n=63
KAU
n=139
Nu-Hc
n =24
Cereb
n =84
ADHD
N = 55
ADHD
Normative
N = 84
Non-ADHD
Normative
N = 202
WCS
PADHD
Check
WCS
ANOVA
PADHD
Fishers´
Exact Test
Figure 1. A presentation of the recruitment
and analyses of data in the present study.
ADHD =Attention Deficit Hyperactivity
Disorder; PADHD =Prediction of ADHD;
WCS =Weighed Core Symptoms scale.
54 Objective measures of adult ADHD
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

assessment, psychiatric history, the latest GAF, and informa-
tion about potential medical treatment at the time of the
study were collected from the participants’ clinical records.
Four participants with ADHD were excluded from the analy-
sis because of central stimulant treatment during participa-
tion (n=3) and because of not obtaining the diagnostic
requirements regarding ADHD (n=1), which resulted in a
total number of 55 participants for this group.
The non-ADHD normative group
A majority of the participants in the non-ADHD normative
group (n=139) were recruited with the assistance of
students at the Department of Psychology at Karlstad
University in Karlstad, Sweden. The remaining part of the
group (n=63) was recruited with the assistance of the
Cognitive Neuroscience Centre for Psychiatry at the Uni-
versity of Giessen, Germany. In Karlstad, recruiting was
performed using major employers in the fields of education
(n=48), transportation/industry (n=44), as well as among
students at the University (n=47). In Giessen, all recruit-
ing was performed via major music organizations. The
inclusion criteria for the normative group were an age of
18–65 years and a willingness to sign the informed consent
and complete the study-specific procedures. The exclusion
criterion was any known psychiatric diagnosis. The QbTest-
Plus was performed at the Universities of Karlstad and
Giessen. The procedures for experimental testing with the
QbTest-Plus were the same as described above for the
ADHD group.
The ADHD normative group
The participants in this group had previously completed the
QbTest-Plus as part of a thorough neuropsychiatric assess-
ment at the neuropsychiatric clinic Cereb AB in Stock-
holm, Sweden. The clinical assessments adhered to the
diagnostic criteria outlined in the DSM-IV (APA, 2000).
The unstandardized test report from the QbTest-Plus
served as a basis for the diagnostic evaluation, along with
other instruments of clinical assessment. Apart from the
QbTest-Plus, neuropsychiatric assessments included for
example tests of cognitive functioning, attention, intelli-
gence, ADHD symptomatology, and everyday functioning.
The group was recruited with the assistance of Cereb AB
for methodological purposes, in order to represent an
ADHD normative group during the examination of the
instruments developed in the present study, that is, the
PADHD and the WCS. Because this group is solely a nor-
mative reference group for ADHD in the present study, it is
not reported in the statistical analyses of the results section
of the present study. The procedures for experimental
testing with the QbTest-Plus were the same as described
above for the ADHD group.
Results
Prediction of ADHD
Fisher’s exact test (5% level) with group (non-ADHD
normative group, ADHD group) and the categorical variable,
PADHD (No, Yes), showed a strong significant connection
(p<.001) between the variables, indicating a vast majority
for No in the non-ADHD normative group and a vast major-
ity for Yes in the ADHD group, as well as a Yes minority in
the non-ADHD normative group and a No minority in the
ADHD-group. The effects of the sensitivity and specificity
for the categorical variable of the present study are presented
in Table 3.
Group and gender differences with regard to
dependent variables
A Pillai’s MANOVA (2 ¥2 factorial design) was conducted
with group (non-ADHD normative group, ADHD group)
and gender (men, women) as independent variables, and
hyperactivity, inattention, and impulsivity as dependent vari-
ables. The analysis revealed significant effects for group
(p<.001, h2=.31, power >.99) and for gender (p=.005,
h2=.05, power =.86). However, the analysis did not show a
significant main effect for the interaction of group and
gender (p=.54, h2=.008, power =.20).The results from the
univariate F-tests regarding group and gender are given
below.
Table 3
Effects of Prediction of ADHD (No ADHD,Yes ADHD) for the Non-ADHD
Normative (N=202), and ADHD (N=55) Groups
Group
Prediction of ADHD
No Yes
Frequency % Frequency %
Non-ADHD
normative
167 83 35 17
ADHD 8 14 47 86
Note: There was a significant connection between prediction of ADHD and
group. ADHD =Attention Deficit Hyperactivity Disorder.
PsyCh Journal 55
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

Core symptoms
Univariate F-tests revealed significant effects of group
for hyperactivity, F(1, 253) =31.53, p<.001, Inattention,
F(1, 253) =70.00, p<.001, and Impulsivity, F(1, 253) =
47.45, p<.001, where the non-ADHD normative group
scored higher on all variables compared with the ADHD
group. With regard to gender, univariate F-tests revealed a
significant effect for inattention, F(1, 253) =8.05, p=.005,
but not for hyperactivity or impulsivity (ps>.05). Further
analysis showed that women scored lower on inattention,
indicating higher symptom levels, compared with men. For
means and standard deviations see Table 4.
Weighed Core Symptoms scale
As the WCS is a composite measure, it needed to be
analyzed separately using a two-way ANOVA. The analyses
showed a significant effect of group, F(1, 253) =77.10,
p<.001, but not of gender or the interaction of group and
gender (ps>.05). The descriptive analyses showed that
the non-ADHD normative group scored higher on the WCS
compared with the ADHD group. For means and standard
deviations see Table 4.
Differences of prediction of ADHD with regard to
dependent variables
Subsequent analyses were conducted using a one-way
Pillai’s MANOVA with the categorical variable, PADHD
(no ADHD, yes ADHD), to investigate the relations with
hyperactivity, inattention, and impulsivity. The analysis
revealed significant results with PADHD, p<.001, h2=.51,
power >.99.The results from the univariate F-tests are given
below.
Core symptoms
Univariate F-tests revealed significant effects of hyper-
activity, F(1, 255) =72.30, p<.001, inattention, F(1, 255) =
144.93, p<.001, and Impulsivity, F(1, 255) =64.37,
p<.001, where the no ADHD group scored higher on all
variables compared with the yes ADHD group. For means
and standard deviations see Table 5.
Weighed Core Symptoms scale
The WCS was again analyzed separately using a one-
way ANOVA. The analyses showed a significant effect
for PADHD, F(1, 255) =249.34, p<.001, and descriptive
analyses also showed that the group which was not supposed
to have ADHD, according to the prediction variable, scored
higher on the WCS compared with the group that was pre-
dicted to haveADHD. For means and standard deviations see
Tabl e 5 .
Discussion
The aims of the present study were twofold. First, to examine
the predictive power of the QbTest-Plus in terms of its
sensitivity and specificity for ADHD in adult persons, and
second, to develop a composite measure for the entire ADHD
core symptom triad on the basis of the measures provided
by the QbTest-Plus. Two psychometric measures were devel-
oped in the present study. The first measure was the WCS,
Table 4
Means and Standard Deviations for Hyperactivity, Inattention, Impulsivity, and the WCS with Regard to Group (Non-ADHD Normative Group, N=202;
ADHD Group, N=55) and Gender
Non-ADHD normative group ADHD group
Men (n=114) Women (n=88) Men (n=25) Women (n=30)
M SD M SD M SD M SD
Hyperactivity 73.41 13.23 71.85 13.81 60.72 22.48 56.37 26.04
Inattention 57.63 15.99 52.67 14.17 40.20 15.22 32.37 10.42
Impulsivity 73.10 14.35 74.18 15.45 50.44 31.31 57.57 26.44
WCS 66.40 25.10 61.25 26.34 33.20 26.57 26.67 21.23
Note: The non-ADHD normative group differed from the ADHD-group in all respects. There was no difference between men and women except for inattention. There
was no interaction between group and gender. ADHD =Attention Deficit Hyperactivity Disorder; WCS =Weighed Core Symptoms scale.
Table 5
Means and Standard Deviations for Hyperactivity, Inattention, Impulsivity,
and the WCS with Regard to Prediction of ADHD (No ADHD, Yes ADHD)
No ADHD (n=175) Yes ADHD (n=82)
MSDMSD
Hyperactivity 75.24 11.52 57.73 21.45
Inattention 58.26 14.64 36.40 10.92
Impulsivity 75.63 12.73 56.21 26.12
WCS 70.69 21.48 27.07 18.69
Note: The No group differed from the Yes group in all respects.
ADHD =Attention Deficit Hyperactivity Disorder; WCS =Weighed Core
Symptoms scale.
56 Objective measures of adult ADHD
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

which quantified the amount of ADHD cardinal symptoms.
The second measure was PADHD, which correctly classified
ADHD in a majority of the cases. In this section, the results
of the present study will be discussed in relation to some of
the existing literature. First, the results from the examination
of the sensitivity and specificity will be discussed, followed
by the composite measure, and finally the limitations of the
present study will be considered.
Sensitivity and specificity
In line with another recent study of PADHD (Edebol et al., in
press), most of the ADHD participants and the non-ADHD
normative participants in the present study were correctly
classified using the PADHD, as reflected in 86% sensitivity
and 83% specificity. Apart from ADHD, the previous study
of the PADHD (Edebol et al., in press) also included groups
of participants with bipolar II disorder or borderline person-
ality disorder and participants assessed for but excluded
from a diagnosis of ADHD, as well as normative participants
without ADHD. In that study, the PADHD yielded 87%
sensitivity and 85% specificity for non-ADHD normative
participants, which strengthens the findings of the present
study. Another study (Edebol, Helldin, Holmberg, Gustafs-
son, & Norlander, 2011) investigated the predictive power of
the QbTest-Plus using standardized cut-off points (Q >1.3)
among participants that were being assessed for ADHD.
The analyses with the cut-off points yielded 83% sensitivity
and 57% specificity. However, some of the participants in
that study (Edebol et al., 2011), as well as in the present
study, had psychiatric disorders in addition to ADHD, which
makes interpretation of the results somewhat limited. In this
context, the 87% sensitivity found in the ADHD group with
minimal psychiatric comorbidity (Edebol et al., in press)
both replicates the findings of the present study and supports
the validity of the results as being associated with ADHD,
rather than a psychiatric symptom load in general. The
results for the PADHD in the present study are thus con-
firmed by the findings on well-defined ADHD samples
without severe comorbidity (Edebol et al., in press). The fact
that other clinical groups with bipolar II, borderline, and
disconfirmed ADHD yielded lower levels of sensitivity (i.e.,
36–41%) than the ADHD group (Edebol et al., in press) also
strengthens the result from the present study of the PADHD
being associated with ADHD more than with psychiatric
disorders sharing symptoms with ADHD. A contribution of
the present study when it comes to estimating the predictive
power of the QbTest-Plus is that PADHD was evaluated on a
well-assessed and convincing pool of patients with ADHD.
The clinical assessments were thorough, well-documented,
and completed prior to experimental testing. Most of the
cases were correctly classified using the PADHD despite the
additional psychiatric disorders. As ADHD is commonly
associated with additional psychiatric disorders that may
confound clinical assessment, the predictive power in terms
of both sensitivity and specificity are vital for psychometric
instruments investigated for clinical practice.
The results of the QbTest-Plus in the present study may be
compared with similar instruments in terms of sensitivity and
specificity. Walker, Shores, Trollor, Lee, and Sachdev (2000)
investigated the predictive values of frequently used neuro-
psychological tests for adults withADHD. Significant effects
were found for the number of omission errors on the CPT and
a few other neuropsychological tests. The predictive values
for omission errors with regard to healthy controls were 63%
sensitivity and 90% specificity, and with regard to clinical
controls they were 63% sensitivity and 60% specificity. The
level of sensitivity found forADHD in the Walker et al. study
(i.e., 63%) was relatively low compared with the present
study, but the level of specificity for the nonaffected partici-
pants (i.e., 90%) was in line with the present study. Walker
et al. found the most prominent aspect of ADHD during CPT
testing to be inattention, as measured using omission errors.
In the general literature, attention impairments have consis-
tently been reported during the CPT performance of adults
with ADHD (Johnson et al., 2001), whereas impulsivity has
been less consistent (Losier et al., 1996). Likewise, in the
present study, inattention was the most common and impul-
sivity the least common feature of ADHD performance. The
most specific feature of ADHD in our study, regardless of
the diagnostic subtype, was motor activity, which is also
consistent with studies that have applied MTS or actigraphy
measures in order to operationalize hyperactivity as motor
activity (Boonstra et al., 2007; Lis et al., 2010; Polcari et al.,
2010; Teicher et al., 1996).
Another large-scale study (Woods, Lovejoy, Stutts, Ball,
& Fals-Stewart, 2002) combined several neuropsychologi-
cal measures of verbal fluency, cognitive flexibility, divided
attention, information processing speed, freedom from dis-
tractibility, and the recall component of word list learning in
order to increase the diagnostic accuracy for adult ADHD.
Depending on the cut-off point, sensitivity ranged from
73–85% and specificity from 69–77%. However, these pre-
dictive values are generally somewhat lower or similar to that
of the PADHD in the present study. Recently, a systematic
PsyCh Journal 57
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

review was conducted for the psychometric properties of the
most common self-rating scales for adult ADHD (Taylor,
Deb, & Unwin, 2011). The review found Conner’s Adult
ADHD Rating Scale (CAARS) to be one of the most accu-
rate scales, presenting 82% sensitivity and 87% specificity.
Another common scale, the Adult ADHD Self-Report Scale
(ASRS) had among the better psychometric properties of all
the investigated scales, presenting 39–69% sensitivity and
88–100% specificity. Compared with the literature on instru-
ments and screening methods for adult ADHD, the predictive
values of the PADHD in the present study suggest that
a laboratory measure applying combined CPT and MTS
presents similar or better psychometric properties than
commonly used screening instruments for adult ADHD.
Moreover, recent studies (Walker et al., 2000; Woods et al.,
2002) also suggest that the predictive values reported for the
PADHD in the present study are more reliable for the correct
classification of ADHD than solitary CPT measures. Finally,
a combination of CPT and MTS measures like the one inves-
tigated in the present study provides unique aspects of cog-
nitive as well as psychomotor aspects of the disorder, which
is both psychometrically useful and characteristic of the
disorder in adulthood (Boonstra et al., 2007; Lis et al., 2010;
Polcari et al., 2010; Teicher et al., 1996). Further diagnostic
and treatment implications may therefore be investigated.
The composite measure
The second aim of the present study was to develop a com-
posite measure for the entire ADHD core symptom triad on
the basis of the measures provided by the QbTest-Plus. This
was possible by means of the WCS. The scale separated the
majority of the participants with ADHD from the majority
of the participants without ADHD. The participants with
ADHD had lower scores on the WCS (indicating higher
levels of total symptoms) than the participants without
ADHD, who had higher scores on the WCS (indicating lower
levels of total symptoms). The WCS was developed using
Qb-Test raw scores from the cardinal symptom measures
of hyperactivity, inattention, and impulsivity. The scale was
transformed, using visual binning with ten cut-points, into
percentages where 0 indicated the maximum amount of
ADHD cardinal symptoms and 100 indicated the complete
absence of the symptoms. Interestingly, hyperactivity was the
measure with the most diagnostic specificity, occurring fre-
quently and most exclusively in the ADHD group regardless
of the diagnostic subtype. Inattention was the most common
symptom for both groups, which gives this measure a par-
ticular significance for diagnostic sensitivity. Impulsivity is
probably the measure with the least sensitivity. It occurred
infrequently in the ADHD group, but when it did so, it was
often in extreme forms and usually along with other cardinal
symptoms, consequently not adding any exclusive informa-
tion for the detection of ADHD, altogether rendering low
specificity. This relative significance of the cardinal symp-
toms was emphasized when constructing the WCS, because
symptoms were given various weights, which is in line with
the literature on the implications of core symptoms for the
clinical diagnosis of ADHD (Murphy & Barkley, 1996).
In line with previous research (Edebol et al., in press;
Lis et al., 2010; Polcari et al., 2010), both the raw scores and
the psychometric instruments of the present study confirmed
that the level of subtle motor activity was highly marked in
subjects with ADHD compared with subjects without the
disorder. Inattention was another strong marker of ADHD,
but not enough to identify and separate a significant pro-
portion of the ADHD group from the non-ADHD norma-
tive group. Conventional CPT measures of inattention and
impulsivity have previously been reported to lack high
enough levels of sensitivity and specificity to correctly
classify ADHD among adults (Corbett & Stanzcak, 1999;
Seidman et al., 1997; Walker et al., 2000; Wood et al., 2002).
Importantly, neither of the core symptom measures in the
present study solely identified a significant number of sub-
jects with ADHD. Only the composite measure generated
significant differences because, unlike the core symptom
measures, the WCS is calibrated with the entire clinical
ADHD phenomenon and the relative impact of behavior
manifestations.
The present study did not intend to investigate the
PADHD and the WCS across the diagnostic subtypes of
ADHD. Thus, the sample was not selected to be representa-
tive of the clinical phenomenon with regard to its relative
proportions of diagnostic subtypes. However, it is worth
mentioning that the majority of the ADHD participants in
the present study were correctly classified using the PADHD
and marked as impaired on the WCS regardless of their
diagnostic subtype. The proportion of the ADHD predomi-
nantly inattentive subtypes in the present study (22%) was,
however, lower than the clinical prevalence in general, that
is, 37% (Millstein, Wilens, Biederman, & Spencer, 1997).
The low total number of participants with ADHD in general
(n=55) and with the inattentive subtype in particular
(n=11), suggests that additional studies with more repre-
sentative samples are needed in order to investigate the
58 Objective measures of adult ADHD
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

present results with regard to the diagnostic subtypes of the
clinical population with ADHD in general. As the hyperac-
tivity measure has been emphasized in the present study, it
is vital to investigate the levels of sensitivity with regard
to well-defined and clinically representative samples of the
ADHD diagnostic subtypes.
Even though the PADHD and the WCS are dependent on
the same QbTest-raw scores, they were developed indepen-
dently of each other. Statistical analyses with the PADHD
and the WCS indicate that negative prediction was related
to higher scores on the scales (indicating lower symptom
levels), whereas positive prediction was related to lower
scores on the scales (indicating higher symptom levels).
Consequently, measures of ADHD (the WCS) and prediction
of ADHD (the PADHD) were associated with each other and
with actual ADHD (clinical diagnosis) in a majority of cases.
The present study also developed three separate core
symptom scales intended for the patient and the clinician to
use when illustrating and discussing symptom severity, as
well as for monitoring treatment programs and progression.
The core symptoms scales and the composite scale represent
dimensional approaches to ADHD diagnosis and treatment.
The behavioral measures are in line with the current clini-
cal perspectives on ADHD and enable quantification of
symptom severity and validation of subjective behavior
ratings made by patients and family members. Both from
the empirical scientific quarter and from literature reviews
of adult ADHD (Epstein, Johnson, Varia, & Conners, 2001)
using recent neuropsychological and neuroimaging perspec-
tives, a heavier weight on performance-based assessments
has been suggested for clinical and research methodologies
(Doyle et al., 2005; Frazier et al., 2004). This would prefer-
ably include methodologies with empirically derived and
age-sensitive neuropsychological tests and behavioral mea-
sures that potentially differentiateADHD from other psychi-
atric disorders with shared symptoms with regard to ADHD.
The results of the present study suggest that the behaviors
of ADHD may be communicated with the WCS, which is
a composite measure of ADHD. The WCS was constructed
in order to recognize the levels of malfunctioning related
to ADHD and, as such, it may be used for diagnostic pur-
poses. But a continual measure of ADHD communicates
not only degrees of dysfunction, but also, it is hoped, positive
improvements made during treatment programs and clinical
interventions. And to better understand the true meaning of
a certain measure, experiences of personal development and
management are essential parts of the interpretation.
Cognitive and behavioral aspects of ADHD seem to occur
on a continuum, and diagnostic recognition is being defined
in clinical rather than statistical terms. According to the
WCS it seems meaningful to look at the continuum across
groups participating in the current study, not only for the
purpose of finding an optimal cut-off point, but to gain a
perspective of the broader formations of the disorder as well.
The prevalence ofADHD in the adult normal population has
previously been reported to be approximately 5% (DuPaul
et al., 2001; Murphy & Barkley, 1996). This may, however,
be restricted due to the diagnostic requirements being
fixed across the lifespan. Assuming instead the principle that
ADHD exists on a continuum, the prevalence of ADHD in
the non-ADHD normative group of the present study may
indicate sensitivity also towards the intermediate zones on
the continuum. A full 100% specificity is perhaps not attain-
able, even when using an “objective” measure of ADHD.
Perhaps the continuum of the current study illustrates that
the term “objective” relates to the standardized procedures
of the test and the unbiased interpretations of the measures
rather than a 100% precise test of the disorder. The non-
ADHD normative group was less well investigated than the
ADHD group, however, and accordingly its characteristics,
such as the educational, social, and employment status, were
not fully identified, so the level of match with the ADHD
group is unclear. However, as opposed to reporting the stan-
dardized cut-off points for the test or taking into account
only the isolated symptom measures, the present study sug-
gests that more accurate interpretations of ADHD are facili-
tated when standardized interpretations like the PADHD and
the composite WCS are applied, which is also in line with the
test objectives.
In order to develop standardized interpretations of the
WCS more suitably, the gender aspect could be taken into
consideration, as the present study as well as another study
(Edebol et al., in press) observed that women generally
showed statistically significant higher levels of inattention
than men. This finding may be explained, for example, by a
bias in the matching or selection criteria for the groups, or
it may be an artifact of diagnostic tendencies for women
being more dysfunctional than for men when receiving a
diagnosis of ADHD, which is also reflected in the current
male-referenced diagnostic standards (Barkley, 2006). The
finding is, however, not consistent with other studies of CPT
performance in ADHD (Gaub & Carlson, 1997; Gershon,
2002; Newcorn et al., 2001), where instead women are found
to exhibit less or similar degrees of inattention then men.
PsyCh Journal 59
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

Prospective studies of the QbTest-Plus should be attentive to
potential gender effects and biases so that the standards
should be adjusted accordingly if the observations are con-
firmed. Also, the WCS and the PADHD should be developed
with regard to treatment and clinical intervention programs
so that additional tests and measures of positive improve-
ment may be taken into account for future studies.
Limitations
The limitations of the present study concern the comorbid
psychiatric disorders in the group with ADHD. Most psychi-
atric disorders are potential biases when measuring atten-
tion, impulsivity, and even motor activity. The proportion
of participants with the ADHD predominantly inattentive
subtype was 22%, which is slightly low for clinical samples
of adult ADHD in general. Another obvious limitation con-
cerns the potential bias of psychotropic medication. Yet
another limitation concerns the non-ADHD normative group
because participation was based on personal interest, which
may contribute to a sampling bias. Finally, it is not clear to
what degree the non-ADHD normative group is characteris-
tic of the population in general, and the lack of certain
demographic data for this group also limits the comparison
with the ADHD group.
Summary
The Quantified BehaviorTest Plus was examined with regard
to ADHD cardinal symptoms. Hyperactivity, measured in
motor activity, was the most specific symptom of ADHD.
Inattention was the most sensitive and impulsivity the least
sensitive symptom ofADHD when measured with a continu-
ous performance test. ADHD was measured on a 10-point
composite scale called the Weighed Core Symptoms scale,
and predicted using the variable Prediction of ADHD in the
majority of cases. The participants with ADHD had lower
scores on the WCS (indicating higher levels of total symp-
toms), and participants without ADHD had higher scores on
the WCS (indicating lower levels of total symptoms). The
predictive values were similar to or higher than traditional
measures of ADHD, such as behavior rating scales and neu-
ropsychological tests. The study had limitations concerning
psychiatric comorbidity and psychotropic medication in
the group with ADHD, and some demographic data was not
available to facilitate the matching process of the non-
ADHD normative group.
Conflict of interest
The authors declare that they have no competing interests.
Authors’ contributions
H. E. contributed to the acquisition and analysis of the
data and the draft of the manuscript, L. H. contributed to the
acquisition of data, the design of the study, and the draft
of the manuscript, and T. N. contributed to the design of
the study, the analysis of the data, and the draft of the
manuscript.
Acknowledgments
This project was supported by unrestricted grants from
the County Council (Landstinget) of Värmland, LiV,
Sweden, and Janssen-Cilag AB, Sollentuna, Sweden. We
would like to thank the Psychiatric clinics in the County
Council of Värmland and in the Nu-Health Care,Trollhättan,
Sweden, for recruiting participants and for supporting the
study, and we would like to thank all of the participants who
joined the study. The authors also acknowledge the excellent
technical assistance of Britt-Marie Hansson, Carolyn Isaks-
son, Kerstin Ling, Fredrik Ulberstad, Hans Boström, and
Petter Knagenhjelm.
References
American Psychiatric Association. (2000). Diagnostic and statisti-
cal manual of mental disorders (4th ed. text revision). Washing-
ton, DC: Author.
Barkley, R. A. (2006). Attention Deficit Hyperactivity Disorder: A
handbook for diagnosis and treatment (3rd ed.). New York: The
Guilford Press.
Barkley, R. A., Murphy, K. R., & Kwasnik, D. (1996). Psychologi-
cal adjustment and adaptive impairments in young adults with
ADHD. Journal of Attention Disorders,1, 41–54. doi:10.1177/
108705479600100104
Boonstra, A. M., Kooij, J. J., Oosterlaan, J., Sergeant, J. A.,
Buitelaar, J. K., & Van Someren, E. J. (2007). Hyperactive night
and day? Actigraphy studies in adult ADHD: A baseline com-
parison and the effect of methylphenidate. Sleep,30, 433–442.
Boonstra, A. M., Oosterlaan, J., Sergeant, J. A., & Buitelaar, J. K.
(2005). Executive functioning in adult ADHD: A meta-analytic
review. Psychological Medicine,35, 1097–1108. doi:10.1017/
S003329170500499X
Brocki, K. C., Tillman, C. M., & Bohlin, G. (2010). CPT perfor-
mance, motor activity, and continuous relations to ADHD
symptom domains: A developmental study. European Journal
60 Objective measures of adult ADHD
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

of Developmental Psychology,7, 178–197. doi:10.1080/
17405620801937764
Charles, L., Schain, R. J., Zelniiker, T., & Guthrie, D. (1979).
Effects of methylphenidate on hyperactive children’s ability to
sustain attention. Pediatrics,64, 412–418.
Corbett, B., & Stanzcak, D. E. (1999). Neuropsychological perfor-
mance of adults evidencing attention deficit hyperactivity
disorder. Archives of Clinical Neuropsychology,14, 373–387.
doi:10.1016/S0887-6177(98)00037-7
Corkum, P. V., & Siegel, L. S. (1993). Is the continuous
performance task a valuable research tool for use with children
with attention deficit hyperactivity disorder? Journal of Child
Psychology and Psychiatry,34, 1217–1239. doi:10.1111/j.1469-
7610.1993.tb01784.x
Douglas, V. I. (1972). Stop, look and listen. The problem of sus-
tained attention and impulse control in hyperactive and normal
children. Canadian Journal of Behavioral Science,4, 259–282.
doi:10.1037/h0082313
Doyle, A. E., Faraone, S. V., Seidman, L. J., Willcutt, E. G.,
Nigg, J. T., Waldman, I. W., . . . Biederman, J. (2005). Are
endophenotypes based on measures of executive functions
useful for molecular studies of ADHD? Journal of Child
Psychology and Psychiatry,46, 774–803. doi:10.1111/j.1469-
7610.2005.01476.x
DuPaul, G. J., Schaughency, E. A., Weyandt, L. L., Tripp, G.,
Kiesner, J., Ota, K., & Stanish, H. (2001). Self-report of ADHD
symptoms in university studies: Cross-gender and cross-national
prevalence. Journal of Learning Disabilities,34, 370–379.
doi:10.1177/002221940103400412
Edebol, H., Helldin, L., Holmberg, E., Gustafsson, S., & Norlander,
T. (2011). In search for an objective measure of hyperactivity,
impulsivity and inattention in adult attention deficit hyperactiv-
ity disorder using the quantified behavior test plus. Europés
Journal of Psychology,7, 443–457.
Edebol, H., Helldin, L., & Norlander, T. (in press). Objective mea-
sures of behavior manifestations in adult ADHD and differen-
tiation from participants with bipolar II disorder, borderline
personality disorder, participants with disconfirmed ADHD as
well as normative participants. Clinical Practice and Epidemi-
ology in Mental Health.
Epstein, J. N., Johnson, D. E., Varia, I. M., & Conners, C. K. (2001).
Neuropsychological assessment of response inhibition in adults
with ADHD. Journal of Clinical and Experimental Neuropsy-
chology,23, 362–371. doi:10.1076/jcen.23.3.362.1186
Frazier, T. W., Demaree, H. A., & Youngstorm, E. A. (2004). Meta-
analysis of intellectual and neuro-psychological test performance
in attention-deficit/hyperactivity disorder. Neuropsychology,18,
543–555. doi:10.1037/0894-4105.18.3.543
Gaub, M., & Carlson, C. L. (1997). Gender differences in ADHD:
A meta-analysis and critical review. Journal of the American
Academy of Child and Adolescent Psychiatry,36, 1036–1045.
doi:10.1097/00004583-199708000-00011
Gershon, J. (2002). A meta-analytic review of gender differences
in ADHD. Journal of Attention Disorders,5, 143–154. doi:
10.1177/108705470200500302
Grodzinsky, G. M., & Barkley, R. A. (1999). Predictive power
of frontal lobe tests in the diagnosis of attention-deficit
hyperactivity disorder. Clinical Neuropsychologist,13, 12–21.
doi:10.1076/clin.13.1.12.1983
Hervey, A. S., Epstein, J. N., & Curry, J. F. (2004). Neuropsychol-
ogy of adults with attention deficit/hyperactivity disorder:
A meta-analytic review. Neuropsychology,18, 485–503.
doi:10.1037/0894-4105.18.3.485
Johnson, D. E., Epstein, J. N., Waid, R., Latham, P. K., Voronin, K.
E., & Anton, R. (2001). Neuropsychological performance
deficits in adults with attention deficit/hyperactivity disorder.
Archives of Clinical Neuropsychology,16, 587–604. doi:
10.1016/S0887-6177(00)00070-6
Kaplan, R. F., & Stevens, M. C. (2002). A review of adult ADHD:
A neuropsychological and neuroimaging perspective. CNS
Spectrums,7, 355–362.
Kessler, C. R., Adler, L., Ames, M., Demler, O., Faraone, S., Hiripi,
E., . . . Walter, E. E. (2005). The world health organization adult
ADHD self-report scale (ASRS): A short screening scale for use
in the general population. Psychological Medicine,35, 245–256.
doi:10.1017/S0033291704002892
Kessler, R. C., & Üstün, T. B. (2005). The world mental health
(WMH) survey initiative version of the world health organiza-
tion (WHO) composite international diagnostic interview
(CIDI). The International Journal of Methods in Psychiatric
Research,13, 93–121. doi:10.1002/mpr.168
Lis, S., Baer, N., Stein-en-Nosse, C., Gallhofer, B., Sammer, G., &
Kirsch, P. (2010). Objective measurement of motor activity
during cognitive performance in adults with attention deficit/
hyperactivity disorder. Acta Psychiatrica Scandinavia,122,
285–294. doi:10.1111/j.1600-0447.2010.01549.x
Losier, B. J., McGrath, P. J., & Klein, R. M. (1996). Error patterns
on the continuous performance test in non-medicated and medi-
cated samples of children with and without ADHD: A meta-
analysis review. Journal of Child Psychology and Psychiatry
and Allied Disciplines,37, 971–987. doi:10.1111/j.1469-
7610.1996.tb01494.x
Luborsky, L. (1962). Clinicians’ judgments of mental health.
Archives of General Psychiatry,7, 407–417. doi:10.1001/
archpsyc.1962.01720060019002
McGee, R. A., Clark, S. E., & Symons, D. K. (2000). Does the
Conners’ continuous performance test aid in ADHD diagnosis?
Journal of Abnormal Child Psychology,28, 415–424. doi:
10.1023/A:1005127504982
Millstein, R. B., Wilens, T. E., Biederman, J., & Spencer, T. J.
(1997). Presenting ADHD symptoms and subtypes in clinically
referred adults with ADHD. Journal of Attention Disorders,2,
159–166. doi:10.1177/108705479700200302
Murphy, K., & Barkley, R. A. (1996). Prevalence of DSM-IV
symptoms of ADHD in adult licensed drivers: Implications for
clinical diagnosis. Journal of Attention Disorders,1, 147–161.
doi:10.1177/108705479600100303
Newcorn, J. H., Halperin, J. M., Jensen, P., Abikoff, H. B., Arnold,
E., Cantwell, D. P., . . . Vitiello, B. (2001). Symptom profiles in
children with ADHD: Effects of comorbidity and gender.
Journal of the American Academy of Child and Adolescent Psy-
chiatry,40, 137–146. doi:10.1097/00004583-200102000-00008
Pliszka, S. R. (1992). Comorbidity of attention-deficit hyperactivity
disorder and overanxious disorder. Journal of the American
Academy of Child and Adolescent Psychiatry,31, 197–203.
doi:10.1097/00004583-199203000-00003
Polcari, A., Fourligas, N., Navalta, C., & Teicher, M. H. (2010).
Hyperactivity persists in male and female adults withADHD and
PsyCh Journal 61
© 2012 The Institute of Psychology, Chinese Academy of Sciences and Blackwell Publishing Asia Pty Ltd

remains a highly discriminative feature of the disorder. Poster
presented at the 57th annual meeting of the American Academy
of Child and Adolescent Psychiatry, New York, NY. Retrieved
from http://www.biobdx.com/wp-content/uploads/2011/03/
2010-AACAP-Teicher.pdf
QbTech AB. (2010a). QbTest plus clinical manual. Gothenburg,
Sweden: Author.
QbTech AB. (2010b). QbTest technical manual. Gothenburg,
Sweden: Author.
Riccio, A. C., & Reynolds, R. C. (2001). Continuous performance
tests are sensitive to ADHD in adults but lack specificity—A
review and critique for differential diagnosis. Annals of the New
York Academy of Sciences,931, 113–139. doi:10.1111/j.1749-
6632.2001.tb05776.x
Rosvold, E. H., Mirsky, F. A., Sarason, I., Bransome, D. E., &
Beck, H. L. (1956). A continuous performance test of brain
damage. Journal of Consulting Psychology,20, 343–350.
doi:10.1037/h0043220
Schoechlin, C., & Engel, R. R. (2005). Neuropsychological
performance in adult attention-deficit hyperactivity disorder:
Meta-analysis of empirical data. Archives of Clinical Neuropsy-
chology,20, 727–744. doi:10.1016/j.acn.2005.04.005
Seidman, L. J., Biederman, J., Faraone, S. V., Weber, W., &
Ouellette, C. (1997). Toward defining a neuropsychology
of attention deficit hyperactivity disorder: Performance of chil-
dren and adolescents from a large clinically referred sample.
Journal of Consulting and Clinical Psychology,65, 150–160.
doi:10.1037/0022-006X.65.1.150
Sykes, D. H., Douglas, V. I., & Morgenstern, G. (1973). Sustained
attention in hyperactive children. Journal of Child Psychology
and Psychiatry and Allied Disciplines,14, 213–220. doi:
10.1111/j.1469-7610.1973.tb01189.x
Taylor, A., Deb, S., & Unwin, G. (2011). Scales for the identifica-
tion of adults with attention deficit hyperactivity disorder
(ADHD): A systematic review. Research in Developmental Dis-
abilities,32, 924–938. doi:10.1016/j.ridd.2010.12.036
Teicher, M. H., Ito, Y., Glod, C. A., & Barber, N. I. (1996). Objec-
tive measurement of hyperactivity and attentional problems in
ADHD. Journal of American Academy of Child and Adolescent
Psychiatry,35, 334–342. doi:10.1097/00004583-199603000-
00015
Tuisku, K., Virkkunen, M., Holi, M., Lauerma, H., Naukkarinen, H.,
Rimon, R., & Wahlbeck, K. (2003). Antisocial violent offenders
with attention deficit hyperactive disorder demonstrate akathisia-
like hyperactivity in three-channel actometry. Journal of Neuro-
psychiatry and Clinical Neuroscience,15, 194–199. doi:10.1176/
appi.neuropsych.15.2.194
Walker, A. Y., Shores, A. E., Trollor, J. N., Lee, T., & Sachdev, P. S.
(2000). Neuropsychological functioning of adults with atten-
tion deficit hyperactivity disorder. Journal of Clinical and
Experimental Neuropsychology,1, 115–124. doi:10.1076/1380-
3395(200002)22:1;1-8;FT115
Woods, S. P., Lovejoy, D. W., Stutts, M. L., Ball, J. D., &
Fals-Stewart, W. (2002). Comparative efficiency of a discrepancy
analysis for the classification of attention-deficit/hyperactivity
disorder in adults. Archives of Clinical Neuropsychology,17,
351–369. doi:10.1016/S0887-6177(01)00120-2
62 Objective measures of adult ADHD
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