Volume 207 - Issue 6
Influence of birth month on the probability of Western Australian children being treated for ADHD
Authors: Martin Whitely, John Phillimore, Leanne Lester and Suzanne Robinson
Med J Aust 2017; 207 (6): 268-269. || doi: 10.5694/mja17.00165
Published online: 18 September 2017
Published online: 18 September 2017
In reply
In reply:
The study that Sciberras and colleagues argue is ideal for examining the attention deficit/hyperactivity disorder (ADHD) late birth date effect analyses the birth date distribution of 391 Victorian children, of which nine received medication.1 In contrast, our study2 reviewed de-identified data on the month and year of birth for all 5937 Western Australian children born between July 1998 and June 2008, who received at least one Pharmaceutical Benefits Scheme subsidised ADHD medication in 2013.
We found that the youngest children in WA classrooms were much more likely to be medicated than their older classmates. We cited four large scale international studies with similar findings and, since publication, we have identified another two.3,4 Readers can weigh the findings of these seven peer-reviewed population-wide studies (combined medicated population of over 68 000; total population of over 3 700 000) against the experience of nine medicated children recruited to participate in the research by Sciberras et al.1
Sciberras and colleagues criticised our research for assuming that all WA children entered school at the recommended age. As our article outlined,2 over 98% of WA children start school in the recommended school year intake. To the limited extent that it occurs, delayed entry is most common for children born in June.5 If June is eliminated from our analysis, the late birth date effect progressively shown over the 11 months from July to May is even stronger.
Prescribing rates for children in the seven studies vary between 0.9% and 5.8%. We stand by our assertion that even at relatively low rates of prescribing, this evidence raises serious questions about the validity of ADHD diagnosis. Sciberras and colleagues counter that the WA prescribing rate in our study (1.9%) is well below the “prevalence [of ADHD] of about 5%”. This approximation is actually on the low side of the range of ADHD prevalence rate estimates (1–16%).6 We believe that this massive variation and the birth date effect are predictable consequences of relying on imprecise behavioural diagnostic criteria such as that provided in the Diagnostic and statistical manual of mental disorders published by the American Psychiatric Association.7
Rather than deny the extensive international evidence, Sciberras and colleagues may offer an alternative plausible explanation to age-determined immaturity for the birth date effect. Meanwhile, we intend to undertake research in states with greater school starting age flexibility than WA to determine whether this is associated with a reduction or increase in any birth date effect.
Competing interests
No relevant disclosures.
References
- Efron D, Sciberras E, Anderson V, et al. Functional status in children with ADHD at age 6–8: a controlled community study. Pediatrics 2014; 134: e992-e1000.
- Whitely M, Lester L, Phillimore J, Robinson S. Influence of birth month on the probability of Western Australian children being treated for ADHD. Med J Aust 2017; 206: 85.
- Zoëga H, Valdimarsdóttir UA, Hernández-Díaz S. Age, academic performance, and stimulant prescribing for ADHD: a nationwide cohort study. Pediatrics 2012; 130: 1012-1018.
- Halldner L, Tillander A, Lundholm C, et al. Relative immaturity and ADHD: findings from nationwide registers, parent- and self-reports. J Child Psychol Psychiatry 2014; 55: 897-904.
- Edwards B, Taylor M, Fiorini M. Who gets the “gift of time” in Australia? Exploring delayed primary school entry. Australian Review of Public Affairs 2011; 10: 41-60.
- Goldman LS, Genel M, Bezman RJ, Slanetz PJ. Council on Scientific Affairs, American Medical Association. Diagnosis and treatment of attention-deficit/hyperactivity disorder in children and adolescents. JAMA 1998; 279: 100-1107.
- Whitely M. Attention deficit hyperactive disorder diagnosis continues to fail the reliability and validity tests. Aust NZ J Psychiatry 2015; 49: 497-498.