Relative Age Effect May Skew ADHD Diagnosis, Treatment in Young Children

By Marilynn Larkin

September 22, 2020

NEW YORK (Reuters Health) - In Finland, the youngest children in a classroom are more likely to receive medication for attention deficit hyperactivity disorder (ADHD) than their relatively older classmates due, at least in part, to the "relative age effect" (RAE), researchers say. This effect may lead to the more immature behavior of younger children being inappropriately treated as ADHD.

"Our findings are in line with studies from various countries, regardless of ADHD medication prescription rates," Dr. Miika Vuori of the University of Turku told Reuters Health by email.

"In addition," he said, "the differences in relative maturity are larger during the first school years. Accordingly, we observed that the association between younger relative age and increased risk of being prescribed medication for ADHD was more pronounced at ages 6-8."

"Although there is increased awareness of RAE in ADHD, parents, teachers and clinicians need to take relative age into account when considering the possibility of ADHD in a child," he said. "It is also important to replicate our analyses in the near future in order to examine the extent to which increased awareness is associated with standards in prescribing for children with ADHD."

"Some studies have shown that emotional and behavioral difficulties are stronger predictors of ADHD diagnosis among girls when compared to boys.," he added. Also, "the school environment may play a very important role, as it poses many challenges (e.g., requirement to sit still and listening quietly) for children with ADHD traits."

As reported in Pediatrics, Dr. Vuori and colleagues analyzed ADHD medication use among 7,054 children born in 2005-2007, using an earlier study of RAE among children born 1991-2004 as a baseline (

Finnish children start first grade in the year of their seventh birthday. The cutoff date is December 31, so the relatively youngest are born in September-December, whereas the relatively oldest are born in January-April.

The risk of ADHD medication use increased throughout the year by birth month (i.e., January through April to May through August to September through December).

Among boys born September to December, the association remained stable across cohorts, with a hazard ratio of 1.3. Among girls born in the same period, the HR in the 2005 cohort was 1.4 compared to 1.7 in the 2007 cohort.

"Children in the middle group (i.e., born in May-August) were also more likely to be prescribed ADHD medication than their relatively older classmates independent of gender," Dr. Vuori noted. Specifically, in Cox regression analyses, ADHD medication use was more common for boys born in May to August (HRs approximately 1.1-1.2) and September to December (HRs approximately 1.3), compared with boys born in January to April.

Similarly, among girls born in May to August or September to December 2005, the HRs were 1.3 and 1.4, respectively, compared with girls born in January to April.

Further, in a restricted analytical model that ended at the end of the year of the children's eighth birthday, the HR for boys was 1.5 and for girls, 2.0, among those born in September to December 2007.

Dr. Eric Butter of Nationwide Children's Hospital in Columbus, Ohio, author of a related editorial, commented in an email to Reuters Health, "The authors are making an important contribution by underscoring the value of careful diagnostic assessment for children suspected of having ADHD."

"The best way for us to manage the possibility of RAE," he said, "is to be sure that children can access accurate...evaluations by qualified health professionals who will consider the child's age, prior school history, family context, and many other factors that could be impacting a child's classroom behavior and learning."

For example, while teachers and parents may misattribute a child's behavior problems to ADHD instead of to relative immaturity, he said, it is also possible that "the highly structured demands of school may trigger ADHD symptoms in younger students (that) are noticed for the first time when a child enters school."

"It is also possible that older children's ADHD symptoms could be masked in the structured environment of a classroom when academic demands are relatively low," he added. "In later grades, when academic demands increase and the need for sustained attention increases, these children might only then be referred for diagnosis and treatment."

SOURCE: and Pediatrics, online September 21, 2020.