The PreventDisease.com website highlighted a couple of studies strongly suggesting that the answer is yes. The two studies in question are:
- The importance of relative standards in ADHD diagnoses: Evidence based on exact birth dates, by Todd E. Elder is available in the Journal of Health Economics.
- Measuring Inappropriate Medical Diagnosis and Treatment in Survey Data: The Case of ADHD among School-Age Children, by William N. Evans, Melinda S. Morrill, and Stephen T. Parente is also available in the Journal of Health Economics.
ADHD is a frequently diagnosed behavioral disorder among American students. As the PreventDisease.com folks note, “currently there are no neurological markers for ADHD.” (An excerpt from a great Frontline investigation can be found here.) The website summarizes the findings in this way:
there could be something wrong with the way ADHD is diagnosed in young children in the US, one found that nearly 1 million kids are potentially misdiagnosed just because they are the youngest in their kindergarten year, with the youngest in class twice as likely to be on stimulant medication, while the other study confirmed that whether children were born just before or just after the kindergarten cutoff date significantly affected their chances of being diagnosed with ADHD.
Dr. Todd Elder is an assistant professor of economics at Michigan State University, and his paper
looked at a sample of nearly 12,000 children from the Early Childhood Longitudinal Study Kindergarten Cohort, which is funded by the National Center for Education Statistics. He analysed the difference in ADHD diagnosis and medication rates between the youngest and the oldest children in a kindergarten grade.
He found that the youngest children were significantly more likely to be diagnosed with ADHD and to be prescribed behavior-modifying stimulants such as Ritalin than their older classmates. He told the press that the “smoking gun” was that the diagnoses depended on the children’s age relative to classmates and the teacher’s perceptions of whether they had symptoms.
“If a child is behaving poorly, if he’s inattentive, if he can’t sit still, it may simply be because he’s 5 and the other kids are 6.”
… From his analysis, Elder found that the youngest kindergarten kids were 60 per cent more likely to be diagnosed with ADHD than the oldest in the same grade, and also, by the time those groups reached the fifth and eighth grades, the youngest were more than twice as likely to be on prescription stimulants.
Elder estimated that overall in the US, the misdiagnosis rate is about 1 in 5, that is around 900,000 of the 4.5 million children currently diagnosed with ADHD have been misdiagnosed.
… He found the same definitive pattern both in the case of individual states and when he compared across states.
… “Many ADHD diagnoses may be driven by teachers’ perceptions of poor behavior among the youngest children in a kindergarten classroom,” said Elder, but the “symptoms” that teachers perceive may “merely reflect emotional or intellectual immaturity among the youngest students.”
The second paper, undertaken by researchers at North Carolina State University, Notre Dame and the University of Minnesota, had similar findings.
Co-author Dr Melinda Morrill, a research assistant professor of economics at NC State, told the press that:
“The question we asked was whether children who are relatively young compared to their classroom peers were more likely to be diagnosed with ADHD.”
…They found that kids who were “relatively old-for-grade”, that is those born just after the kindergarten cutoff date, were 25 per cent less likely to have received a diagnosis for ADHD than their “relatively young-for-grade” peers, that is kids born just before the cutoff date.
“This indicates that there are children who are diagnosed (or not) because of something other than underlying biological or medical reasons,” said Morrill.
“We believe that younger children may be mistakenly diagnosed as having ADHD, when in fact they are simply less mature,” she added, drawing the same conclusion as Elder in the first study.
However, she wished to stress that their study is “not downplaying the existence or significance of ADHD in children.”
“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,” she pointed out.