The "Relative Age Effect"

ADHD treatment 48 percent more likely for youngest in class than oldest

(RxWiki News) If your child’s birth date falls on the cusp between academic years, dependent on which side, he or she may face a greater chance of being diagnosed with ADHD. This phenomenon, deemed the “relative age effect,” occurs independent of state or cut-off date.

Canadian researchers sought to understand whether this issue was unique to the US, and unfortunately for Canada, it isn’t.

While their school system follows the calendar year, those born in December were 39 percent more likely to get diagnosed and 48 percent more likely to be prescribed medication for attention deficit hyperactivity disorder (ADHD), according to their investigation.

"Consider relative age in the diagnosis of ADHD."

Lead author, Richard Morrow, is a health research analyst at the University of British Columbia, working with professors and doctors alike to organize the study. “Our analyses show a relative-age effect in the diagnosis and treatment of ADHD in children ages 6-12 years in the province of British Columbia,” they say in their write up.

“Although the influence of relative age on diagnosis and treatment may lessen for older children, we found the effect was present at all ages from 6 to 12 years, for girls and boys alike.”

Data from nearly one million children was compiled through national databases, searching for kids who were six to twelve years old at any point between December 1, 1997 and November 30, 2008.  These children were then grouped based on birth month, and researchers calculated which proportion of each group was diagnosed with ADHD and, of those, which were prescribed ADHD drugs methylphenidate, dextroamphetamine, amphetamine salts or atomoxetine

Their report, published in the Canadian Medical Association Journal (CMAJ), charts ADHD risk with separate tables for boys and girls as well as for diagnosis and treatment. Nevertheless, results were similar across the board: the youngest children in each class were significantly more likely to be diagnosed with ADHD than the oldest.

Morrow explains, “Our study suggests younger, less mature children are inappropriately being labeled and treated,” adding, “It is important not to expose children to potential harms of unnecessary diagnosis and use of medications," as serious health ramifications exist for children being treated for disorders that they do not have. While many treatments are designed to account for chemical imbalances, using these medications on a healthy system could cause similar issues to those they are trying to fix.

The authors express that further research is necessary to determine whether or not the oldest children within a class may be getting under-diagnosed, assuming these “more mature children within each grade are better able to cope with an underlying disorder.”

dailyRx consulted contributing expert Robert Pressman, PhD, Director of Research at the New England Center for Pediatric Research, for his professional opinion on these findings. Dr. Pressman explains, “The article dramatically underscores one of the principal problems with ADHD diagnosis and treatment: ADHD falls into the ‘Eye of the Beholder’ phenomenon of diagnosis.”

Moreover, he says that while medical professionals use a standardized manual for diagnosis (DSM), the symptoms listed occur naturally in humans and “it is a matter of degree.” Since symptoms of ADHD may correlate with characteristics of being less mature, parents and teachers unaware of the relative age effect might have a hard time differentiating.

“With any diagnosis that is dependent upon the judgment of symptoms on a continuum, such as ADHD, the decision is inevitably is based on the examiners' perception,” continues Pressman. “In this case, it is teachers' or parents' perception of to what degree and how many of the symptoms are present compared to a normal population.”

“The findings are reminiscent of the identification of Faux ADHD, first reported last fall in the American Journal of Family Therapy. The ultimate culprit is the ADHD diagnostic process, which lacks objectivity and fails to use adequate ‘rule out’ methodology, i.e., relative age effect.”

The report was funded through by a Catalyst Post-Market Drug Safety and Effectiveness grant provided by the Canadian Institutes of Health Research. Researchers on the study work through the British Columbia Ministry of Health, and no other competing conflicts of interest were reported.

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Review Date: 
March 5, 2012