A new report from the Centers for Disease Control and Prevention says that the number of children diagnosed with attention deficit hyperactivity disorder (ADHD) has been increasing over the last two decades, CBS News reports.

The increasing numbers have prompted concerns about the possibility of over-diagnosis. The report has revealed that one third of the children in the US were diagnosed with ADHD before they turned 6 and 9.5 percent of children in the U.S. between the ages of 3-17 have gotten a diagnosis of ADHD.

For the study, the experts interviewed about 3,000 parents of children who had been diagnosed with ADHD.

"The increased rate is probably tied to kids getting diagnosed younger," Dr. Michael F. Troy, Medical Director of Behavioral Health Services at Children's Hospitals and Clinics of Minnesota, told CBS News.

"In general, there's more awareness of the diagnosis, and once something's accepted as a relatively common diagnosis, it becomes less stigmatized."

Experts feel that in some cases being diagnosed as ADHD, there may be other factors contributing to a child's behavior.

"ADHD is a description of behavior, of how someone presents, not of the etiology [the cause] of it," Troy said.

"You could have a severe cough and it could be because of a lot of different reasons. You could have disregulated behavior and have difficulty focusing and concentrating and it could be ADHD or it could be a combination of other conditions."

Experts also showed concern that over-diagnosis can lead to several other problems, such as overmedication of children.

The study also said that found that for almost twenty percent of the children, family members were the only ones who provided information during the ADHD assessment. According to the American Academy of Pediatrics guidelines, information for ADHD analysis must be collected from various sources, such as teachers, coaches and other adults involved in the child's care.