Earlier this year a major study of almost one million Canadian children found that rates of diagnosed ADHD - as well as use of ADHD medications like Ritalin - were higher in kids born later in the year.
This is strong support for the "immaturity hypothesis" - the idea that some children get a diagnosis of ADHD because they're younger than their classmates at school, and their relative immaturity is wrongly ascribed to an illness. In British Columbia, where the study happened, the cut-off for school entry is December 31st so those born in January will be a year older than their peers born in December.
Worrying stuff. Clearly this is very important, if true. The authors wrote:
These findings raise concerns about the potential harms of overdiagnosis and overprescribing.
Now a new paper published in the Journal of Attention Disorders rejects the immaturity hypothesis: Is the Diagnosis of ADHD Influenced by Time of Entry to School?The authors say no, it isn't - but their data don't actually tell us anything about that.
The esteemed Professor Joseph "Only God Can Judge Me" Biederman and colleagues from Massachusetts General Hospital looked at 562 kids born in August and 529 born in September; the cut-off in the USA is in the summer. Septembers are the oldest in their year, August the youngest.
Of all the children, 55% turned out to have ADHD. There was no difference in rates of ADHD, or the severity of ADHD, between the two groups. Phew! As J-Bo and his East Coast Posse write:
These findings do not support the developmental immaturity hypothesis of ADHD that states that children’s developmental immaturity leads to the inappropriate diagnosis of ADHD. Instead, these findings suggest that children with clinical thresholds of symptoms of ADHD are afflicted with this disorder.
But this just doesn't follow. These results seem to undermine the Canadian data, but they don't. It's comparing apples and oranges.
The difference is that Biederman et al diagnosed all of the cases of ADHD themselves, and they are one of the world's leading ADHD clinical and research teams. All their data show is that being born in August doesn't fool them into inappropriately diagnosing ADHD.
Sadly, not every child has the privilege of being seen at Mass Gen and having "a comprehensive assessment battery that included structured diagnostic interviews; measures of cognitive, interpersonal, familial, and educational functioning; and examination of patterns of familiality of ADHD." These lucky kids got a veritable alphabet soup of psychiatric measures, from the K-SADS-E-IV to the SAICA.
The whole claim of the immaturity hypothesis is that children who are young in their year A) don't actually have more ADHD, but B) tend to get diagnoses when they shouldn't i.e. after an inadaquate assessment, say by a family doctor, on the advice of a parent or teacher. This study confirms A). It says nothing about B).
At best it shows that younger children aren't being referred to Mass Gen just because they're young. But we're not told who makes those referrals, what their qualifications are, or what systems are in place to filter out inappropriate referrals, so this tells us very little; it also seems that many of the kids included here weren't referred on suspicion of ADHD at all, but were enrolled in research studies.
But hey, the Journal of Attention Disorders has a Biostatistical and Methodology Editor, Stephen Faraone. Did he approve of this article? Probably - he's the senior author.
I should stress that none of this proves that "ADHD doesn't exist" or anything so radical. All it means is that ADHD is sometimes diagnosed badly. Which really shouldn't surprise anyone, because doctors are human and make mistakes sometimes.
Biederman, J., Petty, C., Fried, R., Woodworth, K., & Faraone, S. (2012). Is the Diagnosis of ADHD Influenced by Time of Entry to School? An Examination of Clinical, Familial, and Functional Correlates in Children at Early and Late Entry Points Journal of Attention Disorders DOI: 10.1177/1087054712445061
Morrow, R., Garland, E., Wright, J., Maclure, M., Taylor, S., & Dormuth, C. (2012). Influence of relative age on diagnosis and treatment of attention-deficit/hyperactivity disorder in children Canadian Medical Association Journal, 184 (7), 755-762 DOI: 10.1503/cmaj.111619