ADHD Diagnosis Rates Significantly Affected by Birth Dates, School Enrollment Dates

Author:  Brian Jacobsmeyer
Institution:  University of Colorado - Boulder
Date:  November 2010

Think your rambunctious, inattentive child might have Attention Deficit Hyperactivity Disorder (ADHD)? According to a new study, he might simply be acting his age.

A paper recently published in the forthcoming issue Journal of Health Economics indicates that children who are relatively younger than their classmates are more likely to be diagnosed with ADHD.

Because minute differences in birth dates shouldn't make a child more susceptible to ADHD, the authors argue that the large discrepancies in diagnosis rates indicate misdiagnoses. The authors found that children born immediately after the cut-off date for a given grade, who are subsequently older than many of their peers, were 25% less likely to be diagnosed with ADHD than those born right before the cut-off date.

"This indicates that there are children who are diagnosed (or not) because of something other than underlying biological or medical reasons," explains Melinda Morrill, a research assistant professor at North Carolina State and co-author of the paper. "We believe that younger children may be mistakenly diagnosed as having ADHD, when in fact they are simply less mature."

More than half of all diagnoses begin with a teacher's referral. When teachers compare younger students' behavior to that of children who have had an extra year to mature, they can misinterpret the signs of ADHD.

Since the late 1980s, rates of ADHD diagnosis have increased by almost five-fold, raising questions about the reliability of ADHD diagnostic criteria as well as that of the non-specialized doctors who often diagnose it. But can anyone pin down the exact cause of this influx of children who supposedly have ADHD? "That's the $64,000 question," says Dr. William Evans, another co-author of the paper and a Professor of Economics at Notre Dame. "No one really knows for sure."

Morrill, however, cautions that these results shouldn't diminish the importance of ADHD. "We are not downplaying the existence or significance of ADHD in children," she says. "What our research shows is that similar students have significantly different diagnosis rates depending on when their birthday falls in relation to the school year."

Author: Brian Jacobsmeyer

Reviewed by: Natasha Hochlowski, Selby Cull, and Yangguang Ou

Published by: Maria Huang