Objectives. This report summarizes current scientific evidence from the literature in four
areas: the prevalence of attention-deficit/hyperactivity disorder (ADHD) among children 6 to 12
years old in the general population and the comorbidities that might occur with ADHD; the
prevalence of ADHD among children presenting in primary care settings and the comorbidities
that might occur with ADHD; the accuracy of various screening methods in diagnosing ADHD;
and the prevalence of abnormal findings on selected medical screening tests commonly
recommended in evaluating children suspected of having ADHD.
Search Strategy. The evidence on ADHD prevalence and comorbidities was gathered from
published literature identified through searches of MEDLINE and PsycINFO databases, reference
lists in review articles, and from 10 behavioral rating scale manuals. Articles on medical
screening tests were identified through searches of MEDLINE. Additional articles that met
eligibility criteria but were not yet listed in MEDLINE were identified by experts.
Selection Criteria. The diagnosis ofADHD was based on criteria in one ofthe diagnostic
reference standards. Study populations were limited to boys and girls 6 to 12 years of age. Only
studies using general, unselected populations in communities or schools or pediatric/family
practice clinics were used to address the prevalence questions. Data on the performance of
screening tests could come from studies conducted in any setting. Two types of scales were
examined for this report: "ADHD-specific," designed to target ADHD symptoms only, and
"broad-band," designed to screen for various symptoms, including the symptoms found in ADHD
patients. Data sought from medical tests included the prevalence of abnormal findings among
children diagnosed with ADHD. Evidence was admissible if the study from which it came had
representative study populations, comparable control groups and adequate description of
demographic information. Only articles published in English between 1980 and 1997 were used
in the analysis.
Data Collection and Analysis. Two trained specialists independently read each of the
retrieved articles and completed a form which characterized the type of information in the article.
The articles accepted for analysis were each abstracted by trained personnel and the subject
specialist independently abstracted each article. The resulting sets of abstractions (2 abstractions
per article) were compared, with differences discussed and resolved. A multiple logistic
regression model with random effects was used to analyze simultaneously for the effect of age,
gender, diagnostic tool, and setting. The analysis was done using the EGRET software.
Appropriate quality checks were performed.
Main Results. Prevalence of ADHD ranged from 4 to 12 percent in the general, unscreened,
school-age U.S. population. Gender, diagnostic tool, and setting are significant factors in the
prevalence of ADHD, but age is not significant. Boys have higher rates of ADHD than in girls
for all types of ADHD, with the inattentive type most common. Up to one-third of children
diagnosed with ADHD also qualify for one of the five conditions most commonly comorbid with
ADHD: oppositional defiant disorder, conduct disorder, anxiety disorder, depressive disorder or
learning disorders.
The prevalence of ADHD in a pediatric clinic setting varies between two percent of children
and five percent depending on the study. Coexistence of ADHD with other disorders in children
seen by a pediatrician was found in the one study to be 59 percent and in a second to range from
8 to 20 percent, depending on the comorbid condition and whether the informant was the parent
or the child.
Studies of behavioral rating scales showed that the Conners Rating Scale of 1997, contains
two highly effective indices for discriminating between children with ADHD and normal
controls 94 percent of the time. The Barkley School Situations Questionnaire was 86 percent
effective. Medical screening tests to detect a relationship between ADHD and lead levels,
abnormal thyroid function, imaging of brain structures, or EEG abnormalities have not shown
any relationship with ADHD.
Conclusions. The prevalence of ADHD in the general unscreened school-age population was
estimated from 4 percent to 12 percent. In the general, unscreened, school-age population,
prevalence of ADHD co-occurring with other disorders was estimated to be high, based on
results of four studies. Of children diagnosed with ADHD, approximately 35 percent also
qualified for a diagnosis of oppositional defiant disorder, 28 percent qualified for a diagnosis of
conduct disorder, 26 percent qualified for a diagnosis of anxiety disorder, and 18 percent also had
a depressive disorder, and 12 percent had learning disabilities. Prevalence of ADHD in a
pediatric clinic setting varied widely, with few studies available for analysis. The prevalence of
comorbid ADHD in a pediatric clinic setting also varied too widely to draw useful conclusions.
Studies of ADHD-specific rating scales showed that the Conners Rating Scale of 1997 is
highly effective for discriminating between children with ADHD and normal controls. The
studies reviewed could not be used to derive conclusions regarding the effectiveness of broadband
rating scales in distinguishing children with significant problems from children without
significant problems. Evidence does not support the use of tests of such as lead levels, thyroid
function brain imaging, EEG, and neurological screening to screen children suspected of having
ADHD.
