Relative age and specific learning disorder diagnoses: A Finnish population‐based cohort study

Abstract

Background: Being among the youngest in class has previously been associated with attention-deficit/hyperactivity disorder (ADHD) and academic disadvantage, but the relative age effect on learning disorders is less well understood. This study examined whether relatively young children are more likely to be diagnosed with specific learning disorders than their older peers. Methods:The setting included all 388,650 children born singleton in Finland from 1996 to 2002. Cases diagnosed with specific learning disorders in specialized health care by the age of 10 were identified from national registers. Cumulative incidences of specific learning disorders and the corresponding incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were calculated for each birth month compared to January.Results: During follow-up, 3162 (0.8% of 388,650) children were diagnosed with a specific learning disorder. Children born in December displayed higher cumulative incidences for specific learning disorders than children born in January (IRR: 1.77, 95% CI: 1.50-2.11). The findings were similar for girls (IRR: 2.01, 1.44-2.83) and boys (IRR: 1.70, 1.39-2.08). ADHD did not explain the association, as the IRR for the youngest children with specific learning disorders and ADHD was 1.59 (1.13-2.26) compared to those without ADHD (IRR: 1.84, 1.51-2.24). Conclusions:Relatively younger children in Finnish schools were more likely to be diagnosed with a specific learning disorder by the age of 10. Increased awareness of how relative age differences affect the likelihood for children to be diagnosed with specific learning disorders is needed among parents, clinicians, and teachers.

Quantitative and molecular genetics of child and adolescent mental health disorders: Recent advances, knowledge gaps and directions for future research

“…Such an approach would not only increase sample size substantially, but also facilitate new research directions, such as studies of largely understudied childhood mental conditions and the biological basis of treatment response. The publication by Arrhenius et al (2021) in this issue of JCPP Advances highlights the value of using electronic health records from national registers to ascertain a large number of individuals with a diagnosis of specific learning disorders (N = 3162).…”

Referral bias for specific learning disorders? The wide‐ranging challenges for the youngest in class – Commentary on Arrhenius et al. (2021)

“…The relative age effect captures the observation that children who are younger than most of their peers in the same class are at a disadvantage in relation to a range of outcomes. Arrhenius et al (2021) point out that this phenomenon was described already in 1990; yet, one could argue it has not received the full attention among educational experts and the wider community that it surely deserves. The number of studies reporting relative age effects, for outcomes ranging from academic and sport achievement to the diagnosis of attention-deficit/hyperactivity disorder (ADHD), continues to grow.…”

“…Few methodologically strong studies have examined the relative age effect in relation to specific learning disorders-difficulties with reading, spelling or arithmetic skills that are not due to low general cognitive ability. I was, therefore, pleased to find out that Arrhenius et al (2021) now address this gap, using nationwide data from the Finnish registers. Nationwide registers are an ideal source for examining such effects across very large, representative populations.…”

“…As an example, in the Swedish register data, the prevalence of ADHD diagnosis was 2.8% among the youngest in class (November-December births) and 1.7% among the oldest in class (January-February births) (Halldner et al, 2014). Given such observations and the frequent co-occurrence of ADHD and specific learning disorders, it is important that Arrhenius et al (2021) were able to show that the association of young relative age with specific learning disorders was not due to comorbid ADHD.…”

“…How could we avoid such referral bias? Arrhenius et al (2021) suggest, firstly, that education professionals should 'keep the educational disadvantages of the relatively young in mind when evaluating learning capabilities'. This is important, but may not always be easy to achieve in practice.…”