"In reality, we know that there are fewer teens with a current diagnosis of ADHD than grade-school kids, since at least one-third of kids with ADHD lose the diagnosis [they no longer meet diagnostic criteria] at some point during their adolescence," Adesman said.
In all age groups, boys were about twice as likely as girls to be diagnosed with ADHD, the report found.
"It is unclear why ADHD is more common in boys than girls, though the male predominance appears to be greatest among kids who are hyperactive and impulsive, not just inattentive," said Adesman, who was not involved in the new study. The greater proportion of boys diagnosed with ADHD tends to be especially pronounced among preschoolers, he said.
"This is likely because most of these kids have the 'hyperactive/impulsive' type of ADHD and not the 'inattention only' picture that is more typical of girls and kids in general who present during the later school years," Adesman explained.
More common amongst white kids
White children in the 6-11 and 12-17 age groups were the most likely to have an ADHD diagnosis.
Children with public insurance were also more likely to have an ADHD diagnosis than children with private insurance. Children from lower-income households also were more likely to have a diagnosis, compared to those in wealthier households, the report found.
The number of children diagnosed was lowest among those without health insurance. This suggests that the report may not have captured all the children who have ADHD, Adesman said.
"Limited access to medical care may be one of the reasons for underdiagnosis of ADHD," Adesman said. "Underdiagnosis appears to be a significant problem. The authors cite a different study that suggests many kids who would meet diagnostic criteria for ADHD have never been diagnosed with this disorder."
On the other hand, Adesman noted that other research has suggested that some youth diagnosed with ADHD may actually have been misdiagnosed, so overdiagnosis may be a possibility in some cases, too.
Previous research indicates similar results
Researchers from the U.S. Centers for Disease Control and Prevention found that between 2007 and 2009, an average of 9% of children between the ages of five and 17 were diagnosed with the disorder. This compared with just under 7% between 1998 and 2000.
The survey also indicated that previously notable racial differences in ADHD incidence rates have narrowed considerably since the turn of the millennium.
"We don't have the data to say for certain what explains these patterns, but I would caution against concluding that what we have here is a real increase in the occurrence of this condition," stressed study author Dr Lara J. Akinbami, a medical officer with the National Center for Health Statistics.
The survey was conducted by interviewers from the US Census Bureau through face-to-face and telephone interviews involving a nationally representative group of parents. Basic family demographic information was collected, along with the ADHD status of each household's children.
Although rates rose among both boys and girls, a greater percentage of boys were diagnosed with ADHD overall, rising from roughly 10 percent in 1998-2000 to more than 12% between 2007 and 2009. Across the same time frame, the prevalence rate among girls rose from just below 4% to between 5% and 6%.In addition to the principal findings, the authors were also able to track both financial and geographical trends.
For example, ADHD prevalence hit above-average levels among two groups: households where the family income was below the poverty line (10%) and households where income fell somewhere between the poverty line and double the poverty line (11%).
ADHD is overdiagnosed
SA has one of the highest ADHD medication prescription rates