MENTAL DISORDERS
Children’s mental health problems have emerged
from a long history of misunderstanding and neglect
to become the central concern of an active group of
researchers and practitioners. The last few decades of
the twentieth century witnessed an explosion of
knowledge about the nature of disorders that affect
children, their frequency of occurrence, their devel-
opmental course, and the effectiveness of treatments.
In both children and adults, mental disorders
typically are defined in one of two ways: as a category
or along a dimension. Categorical approaches are
typified by the American Psychiatric Association’s di-
agnostic criteria, as published in the Diagnostic and
Statistical Manual of Mental Disorders: DSM-IV. The
definitions of mental disorders in the DSM-IV are
characterized predominantly by symptom criteria for
diagnoses, as well as by taking into account impair-
ment and, for some disorders, age of onset. For this
approach, clinical interviews are the typical measure-
ment.
In contrast to categorical approaches, dimension-
al approaches emphasize symptoms along a continu-
um from none or few symptoms to clinically
significant levels of symptoms. The dimensional ap-
proach is typically measured by reliable and valid
questionnaires administered to parents, teachers, or
the children under study, with lists of behaviors that
the respondent indicates as being characteristic of the
child, sometimes or somewhat characteristic, or not
characteristic of the child. Children are assigned a
score along the continuum or are indicated as exceed-
ing, or not, an empirically established cutoff for clini-
cally significant levels of behavior problems or, at the
next lower level, of borderline significance.
The mental disorders that children can develop
are commonly divided into two groups: disruptive or
externalizing behavior disorders (e.g., attention-
deficit hyperactivity disorder, conduct problems) and
emotional or internalizing behavior disorders (e.g.,
anxiety, depression). In addition, children also can
develop other disorders that do not fit into this classi-
fication system, such as autism, schizophrenia, and
eating disorders.
An important perspective within which to under-
stand children’s mental disorders is development. By
its nature, children’s behavior fluctuates over time.
One of the biggest challenges for parents and practi-
tioners is to distinguish between normal developmen-
tal changes and the emergence of a disorder (atypical
changes). Development is also an important consider-
ation in determining whether early signs of a disorder
will emerge as a full-blown disorder, develop into a
different disorder, or resolve into healthy function-
ing.
Disruptive or Externalizing Behavior
Disorders
The disruptive or externalizing disorders consist
of attention deficit hyperactivity disorder (ADHD),
conduct disorder, and oppositional defiant disorder.
Because the latter two are both considered disruptive
behavior disorders, they are typically considered to-
gether.Attention Deficit Hyperactivity Disorder
ADHD has as its primary symptoms inattention,
impulsivity, and hyperactivity. Research has shown
that inattention symptoms tend to cluster apart from
symptoms of impulsivity and hyperactivity, while the
latter two tend to cluster together. The DSM-IV main-
tains this distinction by including two sets of symp-
toms. In order to meet diagnostic criteria for ADHD,
the child’s parents or teachers must report the pres-
ence of at least six symptoms of inattention (e.g., is
often easily distracted by extraneous stimuli) or six
symptoms of hyperactivity-impulsivity (e.g., often fid-
gets with hands or feet or squirms in seat). In both
cases, the symptoms must: (1) have been present and
been causing impairment before age seven years; (2)
have been present for six months or more; and (3)
cause clinically significant impairment in terms of in-
terpersonal or academic functioning in two or more
settings and must differ from normal developmental
expectations. Alternatively, behavior rating scales, on
which respondents rate individual symptoms of
ADHD, provide a dimensional, age-sensitive, quanti-
tative assessment of ADHD-related problems, along
with an indication of the level at which the scores are
considered to be indicative of clinically significant
problems.
Although reports vary depending on the criteria
used, with DSM-IV based criteria the estimates of the
incidence of ADHD are about 3 percent to 5 percent
of the general population of children. As with the
other externalizing disorders, it occurs much more
frequently in boys than in girls, with a typical ratio of
six to one in samples attained from treatment settings
and three to one in community samples.
Although some children show signs of ADHD as
early as infancy, for most children the first signs of be-
havior that differs from developmental expectations
emerge between the ages of three and four years. An-
other common time for children to be first identified
is at school entry.
No one knows exactly what causes ADHD. Biolog-
ical factors are likely to include genetic transmission
and pregnancy and birth complications, and may also
include brain injury or lead exposure. Researchers
have found strong evidence for the influence of ge-
netics (although accounting for only 10 percent to 15MENTAL DISORDERS 261