As ADHD and Autism Diagnoses Rose, the Gap Between Diagnosed and Undiagnosed Children Narrowed

Children in Denmark who were diagnosed with ADHD or autism between 2012 and 2022 came to resemble undiagnosed children of the same age more and more closely across that decade, according to a study published Sept. 9 in JAMA Psychiatry. The finding is about who receives a diagnosis, not about the conditions themselves.

Diagnoses of both have risen steeply in many countries, and the authors set out to test whether the children being diagnosed now are the kind of children clinics were picking out ten years earlier. They write in the paper that their results suggest the rise may reflect changes in diagnostic practice or in health care capacity rather than changes in underlying risk alone. They also state that the findings should not be read as evidence that ADHD or autism has become less impairing for an individual.

The team, led by Magnus Elias Tarp and Oleguer Plana-Ripoll at Aarhus University, used Danish national registers to compare 71,317 children and adolescents diagnosed before adulthood with 713,170 undiagnosed children. Each diagnosed child was matched to others of the same sex, birth year, municipality and country of birth. The researchers then compared the two groups on traits recorded before any diagnosis: family situation, birth and early health, and use of health services.

All of those traits separated the two groups, the authors report, and most separated them less as the decade went on. Children with a low birth weight had 1.54 times the odds of being in the diagnosed group at the start of the period and 1.17 times the odds at the end of it. Those figures measure how often a diagnosis and a trait turn up together, not whether one brings on the other.

The narrowing was larger for ADHD than for autism, the paper reports. The link with household income weakened by an average of 6.5% a year for ADHD and 0.7% a year for autism. The narrowing was also more pronounced among children diagnosed in later childhood than among those diagnosed young.