Youngest Kids in Class More Apt to Get ADHD Diagnosis: Study

MONDAY March 5, 2012 -- A new Canadian study provides more evidence that too many young kids may be diagnosed with attention-deficit/hyperactivity disorder, or ADHD, simply because they're younger than their peers in the same classrooms.

Researchers found that nearly 7 percent of boys aged 6 to 12 were diagnosed with ADHD overall, but the percentage ranged from 5.7 percent for those who were the oldest in their grade levels to 7.4 percent for the youngest. There was a similar gap for girls, although they're much less likely to be diagnosed.

The findings, which are similar to those from U.S. studies, don't prove definitively that any kids are being wrongly diagnosed with ADHD or being diagnosed purely because they're younger than their peers.

Still, "it's good for parents to know about this," said study author Richard Morrow, a health research analyst at the University of British Columbia. "In general, the younger you are within your grade, the more likely you are to receive this diagnosis and get treatment."

ADHD is a controversial developmental disorder, and there's been debate about whether it is overdiagnosed. The researchers launched the study to determine whether a student's age in relation to his or her peers may have something to do with the likelihood of diagnosis.

The study authors examined the records of over 930,000 kids in British Columbia who were between the ages of 6 and 12, during the time period from 1997 to 2008. They focused on differences between kids born in January (who'd typically be the oldest in their classes) and December (who'd typically be the youngest due to cut-off dates for school enrollment).

The level of ADHD diagnosis was lowest for kids born early in the year -- the oldest ones in their classes -- and highest for those born later in the year. Kids born in January and December had the lowest and highest rates, respectively: 5.7 percent of boys and 1.6 percent of girls for those born in January, and 7.4 percent of boys and 2.7 percent of girls among those born in December.

Boys born in December were 30 percent more likely to be diagnosed and 41 percent more likely to be treated with ADHD medications than boys born in January were, while the youngest girls were 70 percent more likely to be diagnosed and 77 percent more likely to be treated with medications than the oldest girls were, the study found.

"There is no reason for them to have this kind of difference in their diagnosis," Morrow said. "The way we would interpret that is that there are differences in maturity that are coming into play."

In other words, physicians and teachers may think kids have ADHD when they're actually just younger and less mature than their peers.

Richard Milich, a professor of psychology at the University of Kentucky who studies ADHD, said the findings make sense considering that the disorder is difficult to diagnose, especially at younger ages.

When ADHD becomes an issue, Milich said, parents should be aware of this kind of research and bring it up with their pediatrician or whomever else is appropriate. However, "I hope it doesn't get to the point that people say it's not a valid disorder," he said.

Kids with ADHD "do poorer in school, they're more likely to be left behind and more likely to drop out of school early. Across the board, they are impaired," Milich said. "Whether you want to call it a disorder or not, we know that's what they're at risk for."

The study appears in the March 5 issue of the CMAJ (Canadian Medical Association Journal).

More information

For more about ADHD, visit the U.S. National Library of Medicine.

Posted: March 2012


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