Relative age and ADHD medication

"Youngest children in class 'more likely to be given ADHD drugs'" went the NHS Choices headline that led me to the short report produced by Martin Whitely and colleagues [1] (open-access).

ADHD - attention-deficit hyperactivity disorder - is something of interest to this blog; not least the idea that relative age (age relative to peers in the same school year group) might be an important variable when it comes to at least some diagnoses of the condition (see here).

The Whitely paper draws on data from a research favourite place - Western Australia (WA) - and focused on "the proportions of WA children born in the early and late months of a recommended school-year intake who received at least one Pharmaceutical Benefits Scheme [PBS] prescription for an ADHD medication in 2013."

The results: from a starting population of some 300,000 children, about 6,000 of them (~2%) were in receipt of a state-recognised prescription of an ADHD medication. The article does not actually mention which ADHD medication was given but methylphenidate (a.k.a Ritalin) is listed in the PBS directory and is the typically indicated medication used for ADHD (see here). Boys, we are told, were more likely to be prescribed ADHD medication than girls (2.9% vs. 0.8% respectively).

Then to the headline: when splitting the children into two age groups - 6-10 year olds and 11-15 year olds - researchers noted that those born in June (the last birth month influencing year of school intake) were more likely to be prescribed ADHD medication than those born in July. This trend was noted in both age groups. The conclusion being that the youngest children in a year group at school were more likely to be in receipt of prescribed medication for ADHD compared to older children in the year group.

Alongside the caveats linked to the Whitely report made by NHS Choices, there is a need for further investigation in this area and in particular, whether the results generalise to places outside of just WA. I've already linked to my previous discussion about relative age and ADHD diagnosis/medication (see here again) and from comparisons with the Taiwanese data [2] on this topic, including the fact that Taiwan have a different cut-off month for school entry (August 31). On that basis, yes the trend appears to generalise across geographies...

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[1] Whitely M. et al. Influence of birth month on the probability of Western Australian children being treated for ADHD. MJA. 2017; 206: Feb 6.

[2] Chen MH. et al. Influence of Relative Age on Diagnosis and Treatment of Attention-Deficit Hyperactivity Disorder in Taiwanese Children. J Pediatr. 2016 May;172:162-167.e1.

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Martin Whitely, Leanne Lester, John Phillimore, & Suzanne Robinson (2017). Influence of birth month on the probability of Western Australian children being treated for ADHD The Medical Journal of Australia