New research suggests the rate at which children are being diagnosed with attention hyperactivity disorder has increased by nearly 25 percent in the last decade for reasons that remain largely unknown.
"The important thing we are highlighting is a trend over time," said study author Dr. Darios Getahun, with Kaiser Permanente Southern California's department of research and evaluation. "We are observing an increasing trend among white, Hispanic and African-American children."
Black children saw the biggest bump in the rate of diagnosis -- a relative increase of 70 percent between 2001 and 2010 -- followed by Hispanic and white children. The rate of diagnosis among Asian and Pacific Islander children did not change.
The findings, which were published online in JAMA Pediatrics on Monday, were based on nearly 850,000 electronic health records of 5- to 11-year-olds treated at Kaiser Permanente Southern California. The incidence of newly diagnosed ADHD cases increased from 2.5 percent in 2001 to 3.1 percent in 2010, which represents a relative increase of nearly 25 percent.
Overall, just under 5 percent of the children in the study had a diagnosis for ADHD. That is in line with Centers for Disease Control and Prevention's national estimates that say 8.4 percent of 3- to 17-year-olds (4.7 percent of girls and 12 percent of boys) have been diagnosed with the disorder.
The new study also reflects that gender gap in diagnoses: Overall, boys were three times more likely to be diagnosed with ADHD than girls. But it did suggest that the gap may be closing, particularly among black children. There was a 90 percent relative increase in diagnosed cases of ADHD among black girls over the study period, from slightly more than 1 percent to slightly more than 2 percent.
Tim MacGeorge, director of Children and Adults with Attention Deficit Hyperactivity Disorder's National Resource Center on ADHD, said in an email to HuffPost that "an increase of 100 percent sounds large, but is it large if it means going from 1 to 2 [percent]?"
He added that "In general, girls have often not been diagnosed with ADHD because they've tended to have the 'inattentive type.' It's been easier for the child who is not causing problems with hyperactive or impulsive behavior to be overlooked."
There are three recognized types of ADHD, defined by the symptoms that are strongest in the person with the disorder. Children and adults with the "inattentive type" find it hard to finish tasks, follow conversations or stick to daily routines, while those with the "hyperactive type" may fidget, move constantly and struggle with impulsivity. Individuals who experience both symptom sets equally have the "combined type."
It is unclear what has driven the increase in ADHD diagnosis rates.
The study's authors write that cultural factors may affect who gets diagnosed and treated for the disorder. Asians, for example, were less likely to use mental health services and more likely to discontinue therapy, despite having equal access to health care. Researchers speculate that children born into affluent white families may have higher rates of diagnosis because of an "effort by these highly educated parents to seek help for their children, who may not be fulfilling their expectations with regards to school work."
"This is an important question, and there are probably a variety of answers to it," said MacGeorge. "Although it is unlikely that ADHD is being 'over-diagnosed,' it's important that ADHD be correctly diagnosed."