School Year Bias May Influence ADHD Diagnosis

Researchers have discovered that younger children in elementary schools are more likely to be diagnosed with attention-deficit hyperactivity disorder (ADHD) than their older peers within the same school year.

The European study suggests that adults involved in raising concerns over a child’s behavior, such as parents and teachers, may be mistaking signs of relative immaturity as symptoms of the disorder.

The research was led by a child psychiatrist at the University of Nottingham along with investigators at the University of Turku in Finland. In the study, published in The Lancet Psychiatry, they suggest greater flexibility in school starting dates should be offered for those children who may be less mature than their same school-year peers.

Dr. Kapil Sayal, Professor of Child & Adolescent Psychiatry at the University’s School of Medicine and the Centre for ADHD and Neurodevelopmental Disorders Across the Lifespan at the Institute of Mental Health in Nottingham, was the lead author on the study.

“The findings of this research have a range of implications for teachers, parents, and clinicians. With an age variation of up to 12 months in the same class, teachers and parents may misattribute a child’s immaturity. This might lead to younger children in the class being more likely to be referred for an assessment for ADHD,” said Sayal.

Moreover, parents and teachers as well as clinicians who are undertaking ADHD assessments should keep in mind the child’s relative age. From an education perspective, there should be flexibility with an individualized approach to best meets the child’s needs, contend the researchers.

Evidence suggests that worldwide, the incidence of ADHD among school age children is, at around five percent, fairly uniform. However, there are large differences internationally in the rates of clinical diagnosis and treatment.

Although this may partially reflect the availability of and access to services, the perceptions of parents and teachers also play an important role in recognizing children who may be affected by ADHD, as information they provide is used as part of the clinical assessment.

The new study focused on whether the so-called “relative age effect” — the perceived differences in abilities and development between the youngest and oldest children in the same year group — could affect the incidence of diagnosis of ADHD.

Investigators are concerned that adults may be benchmarking the development and abilities of younger children against their older peers in the same year group and inadvertently misinterpreting immaturity for more serious problems.

Previous studies have suggested that this effect plays an important role in diagnosis in countries where higher numbers of children are diagnosed and treated for ADHD, leading to concerns that clinicians may be over-diagnosing the disorder.

The latest study aimed to look at whether the effect also plays a significant role in the diagnosis of children in countries where the prescribing rates for ADHD are relatively low.

Researchers used nationwide population data from all children in Finland born between 1991 and 2004 who were diagnosed with ADHD from the age of seven years — school starting age — onwards.

In Finland, children start school during the calendar year they turn seven years of age, with the school year starting in mid-August. Therefore, the eldest in a school year are born in January (aged seven years and seven months) and the youngest in December (six years and seven months).

The results showed that younger children were more likely to be diagnosed with ADHD than their older same-year peers; boys by 26 percent and girls by 31 percent.

For children under the age of 10 years, this association got stronger over time — in the more recent years 2004-2011, children born in May to August were 37 percent more likely to be diagnosed and those born in September to December 64 percent, compared to the oldest children born in January to April.

The study found that this “relative age effect” could not be explained by other behavioral or developmental disorders which may also have been effecting the children with an ADHD diagnosis.

Still, the study did have some important limitations; the data did not reveal whether any of the young children were held back a year for educational reasons and potentially misclassified as the oldest in their year group when in fact they were the youngest of their original peers.

The flexibility in school starting date could explain why the rate of ADHD in December-born children (the relatively youngest) were slightly lower than those for children born in October and November.

Another study caveat is that while the records of publicly-funded specialized services — which are free (in Finland) and will probably include most children who have received a diagnosis of ADHD — it will miss those who were diagnosed in private practice.

Source: University of Nottingham/EurekAlert