In general, children and adults with attention deficit/hyperactivity
disorder (ADHD) have trouble concentrating, sitting still and controlling
impulsive behavior. They often struggle with low self-esteem, troubled
personal relationships and poor performance in school or at work. This
Mayo Clinic study concludes that ADHD affects 7.5 percent of school-age
children by age 19, a lower estimate than many other studies because it
is based on more stringent diagnostic criteria.
http://www.mayo.edu/comm/mcr/news_2026.html