(AP) -- A government survey says 1 in 10 U.S. children has ADHD, a sizable increase from a few years earlier that researchers think might be explained by growing awareness and better screening.
ADHD, or attention deficit hyperactivity disorder, makes it hard for kids to pay attention and control impulsive behavior. It's often treated with drugs, behavioral therapy, or both.
The new study found that about two-thirds of the children who have ADHD are on medication.
The estimate comes from a survey released Wednesday that found an increase in ADHD of about 22 percent from 2003 to the most recent survey in 2007-08. The Centers for Disease Control and Prevention interviewed parents of children ages 4 through 17 in both studies.
In the latest survey, 9.5 percent said a doctor or health care provider had told them their child had ADHD. The earlier study found that fewer than 8 percent of kids had been diagnosed with it.
Researchers calculate about 5.4 million kids have been diagnosed with ADHD, which suggests that about 1 million more children have the disorder than a few years earlier.
Scientists don't have clear answers about why there was such a significant increase. Study lead author Susanna Visser of the CDC suggests greater awareness and stepped-up screening efforts as part of the explanation.
"Regardless of what's undergirding this, we know more parents are telling us their children have ADHD," Visser said.
One expert found it hard to believe that so many kids might have ADHD. "It sounds a little high," said Howard Abikoff, a psychologist who is director of the Institute for Attention Deficit Hyperactivity and Behavior Disorders at New York University's Child Study Center.
Other studies have suggested more like 5 percent of kids have ADHD, and there are no known biological reasons for it to be on a recent increase, he added.
Abikoff noted the CDC study is based on parents saying that a health care provider told them their child had ADHD, but it's not known who the health-care provider was or how thorough the assessment was.
ADHD diagnosis is a matter of expert opinion. There's no blood test or brain-imaging exam for the condition. Sometimes reading disabilities or other problems in the classroom cause a teacher or others to mistakenly think a child has ADHD, he said.
The CDC study noted an increase in diagnoses was seen in kids of all races and family income levels, and across all regions of the country except the West. The survey covered 73,000 children.
Of those who had ADHD at the time of the latest survey, about half had a mild form.
The research appears in the CDC publication, Morbidity and Mortality Weekly Report.
Explore further: Blood test spots adult depression
More information: APHA: http://www.cdc.gov/mmwr