The Globe and Mail – Aug. 17, 2010
ADHD: Parents of kids born later in year face tough decision Research suggests immaturity is confused with disorder – and many children could be misdiagnosed
By Tralee Pearce
The youngest children in a kindergarten class are much more likely to be diagnosed with attention-deficit-hyperactivity disorder than their oldest peers, according to two U.S. research studies. The discrepancy would account for about a million misdiagnoses in the United States.
Because all children who turn five within a given 12-month period – starting in September or December in much of North America – attend kindergarten together, ages can vary by up to a year in any class.
Using longitudinal data of about 12,000 children, the study found that the youngest children in kindergarten are 60 per cent more likely to be diagnosed with ADHD than their older peers.
And researchers believe many of the characteristics flagged as signs of ADHD by kindergarten teachers – inattention, hyperactivity and impulsivity – might simply be due to immaturity relative to members of the cohort who are 11 months or more older. “A five-year-old might not be more poorly behaved than the average five-year-old,” said Todd Elder, an economist and the lead author of a University of Michigan study. “But he’s much more poorly behaved than the average six-year-old. There’s a big difference.”
In Michigan, where the cut-off date is Dec. 1, students born on Dec. 1 had much higher rates of ADHD than those born on Dec 2. The former were the youngest in their grade and the latter were the oldest in their grade. August-born kindergarteners in Illinois were much more likely to be diagnosed with the disorder than Michigan kindergarteners born in August of the same year. Dr. Elder said that’s because Illinois’ cut-off date is Sept. 1, so those August-born children were the youngest in their grade, while the Michigan students were not. And those younger kids with diagnoses of ADHD were twice as likely as their older counterparts to be using prescribed stimulants in the 5th and 8th grades.
In a University of Carolina study, lead author Melinda Morrill, an economist, found that children born just after cut-off dates – i.e. the oldest in their classes – were 25 per cent less likely to be diagnosed with ADHD than the children born even a few days earlier, but before the cut-off dates. Both studies are in a forthcoming issue of the Journal of Health Economics.
While it is possible that the older children in the studies are being under-diagnosed, or that going to school early causes ADHD, both researchers say it is more likely that the younger children are being over-diagnosed.