The percentage of children diagnosed with attention deficit-hyperactivity disorder or ADHD in the U.S. has increased in the past decade, according to a new report.

The percentage of children who had ever received a diagnosis of ADHD had increased from about 7 per cent in the 1998-2000 period to 9 per cent in 2007-2009, the August issue of the National Center for Health Statistics Data Brief said. Sheree Fitzgerald at her Macungie, Pa., home with her son, Eddie, who has ADHD. A new report on the prevalence of ADHD in the U.S. suggests it is on the rise, based on a survey of parents. George Widman/Associated Press

Symptoms of ADHD begin in childhood and include inattention, impulsive behavior, and hyperactivity that can affect social interaction and learning. The symptoms often persist into adulthood, Dr. Lara Akinbami of the CDC and her co-authors said.

Children who lived in low-income household or those who lived in the South and Midwest showed the highest reported prevalence.

The estimated prevalence was based on the number of adults who answered "yes" to the question, "Has a doctor or health professional ever told you that your child had Attention Deficit Hyperactivity Disorder (ADHD) or Attention Deficit Disorder (ADD)?"

Since the estimates were based on reports from parents, the findings could be affected by how the accuracy of parents' recall, differences in access to healthcare between groups and willingness to report to a diagnosis of ADHD, the researcher said.

But previous studies suggest that only half of children with symptoms qualifying for a diagnosis of ADHD actually receive one.

"For the present report, it was not possible to discern whether growing prevalence indicates a true change in prevalence or increased detection and diagnosis of ADHD," the authors concluded.

If could be that there actually are more cases of ADHD or that parents, teachers and doctors are now more aware of the condition.