Children with attention-deficit hyperactivity disorder (ADHD) display behavioral
symptoms in three domains: inattention which is characterized by distractibility
and failure to sustain attention in tasks and activities, hyperactivity which refers
to hyperkinesis and motor restlessness, and impulsivity which can be defined as
the tendency to display uncontrolled and disinhibited behaviors (Barkley, 1990).
ADHD is among the most prevalent psychiatric disorders in children andadolescents. Between 5 and 10% of the youths have the psychiatric disorder as described in the Diagnostic and Statistical Manual of Mental Disorders (DSM;
American Psychiatric Association, 1994), and the prevalence in clinical settings
is even higher, with percentages up to 20% (Swanson et al., 1998).