It is the basis for discussions about overdiagnosis. Every now and then, you even read possible explanations that seem more like conspiracy theories. Yet it is a fact: many more children and young people are diagnosed with ADHD or autism today than, say, ten or twenty years ago. In Denmark, for example, the number of diagnoses of both disorders more than tripled between 2000 and 2024. Why am I talking about Denmark? A new study by Magnus Elias Tarp and colleagues in JAMA Psychiatry provides an interesting piece of the puzzle for the question: why?
Are there actually more children with ADHD and autism? Have we become better at recognizing them? Has the threshold for a diagnosis changed? Or do the demands of school and society cause children with certain characteristics to run into problems more quickly nowadays? I can tell you already that the researchers did not manage to answer the why-question definitively. But their work does provide a pretty interesting piece of the puzzle. Their main finding can perhaps be summarized like this: not only has the number of diagnoses changed. Who gets a diagnosis also seems to have changed. But please read on.
The researchers used Danish registers containing data on more than 2.1 million children and young people. For their main analysis, they looked at 71,317 children and young people who received a diagnosis of ADHD and/or autism between 2012 and 2022. They matched each of them with ten children and young people without such a diagnosis, based on sex, year of birth, place of residence, and other factors.
The researchers did not look specifically at the symptoms of ADHD or autism themselves. Instead, they examined 19 characteristics that previous research has linked to a greater likelihood of such a diagnosis. Think, for example, of premature birth and/or low birth weight. They also looked at parental income and education, family circumstances, parental health problems, and prior health care use.
So, what did they find? Children and young people diagnosed with ADHD or autism still differ from children without a diagnosis on many of these characteristics. But… these differences became smaller between 2012 and 2022.
Take low birth weight, for example. In 2012-2013, low birth weight was associated with 54 percent higher odds of a later diagnosis of ADHD or autism. By 2020-2022, this was down to 17 percent. The researchers found a similar pattern for several other characteristics around birth, as well as for socioeconomic characteristics and family circumstances. This means that children and young people who receive a diagnosis today look, on these characteristics, more like those without a diagnosis than they did ten years ago.
This is striking, given the strong increase in the number of diagnoses. In 2012, there were 4,944 new diagnoses in these Danish data; in 2022, there were 9,179. The proportion of girls also increased sharply: from about 32 to 45 percent. Especially for ADHD, the associations with socioeconomic circumstances, family characteristics, and factors around birth became weaker over time. For autism, the changes are generally smaller and less certain.
One possible explanation is that the group eligible for a diagnosis has become broader. Among those receiving a diagnosis today, the characteristics that used to be strongly linked to ADHD or autism are less pronounced. Several things may explain this. ADHD and autism receive more attention. This increased attention may help professionals and parents better recognize signs. Referral options have changed, and health care systems now have greater diagnostic capacity. Professionals may also interpret diagnostic criteria differently.
But according to the researchers, something else may have changed too: when certain characteristics become a problem for us. If schools and society change what they demand from children and young people, the same characteristics may lead to problems in daily functioning more quickly. Therefore, a child does not necessarily need to have ‘more ADHD’ than a comparable child twenty years ago. Still, that child may be more likely to come into the picture for a diagnosis today.
Do realize that this study does not show that children with ADHD or autism have less severe problems today. The researchers did not directly measure these children’s symptoms or their daily functioning. Instead, they looked at characteristics that they could statistically link to a diagnosis. So please, don’t conclude from this study that we are simply diagnosing ‘milder cases’ today. Let alone that diagnoses are being made incorrectly.
What I think the study shows nicely is that the enormous increase in the number of diagnoses does not necessarily mean the underlying population has changed in the same way. The group receiving a diagnosis seems to have changed, at least. Somehow, the study leaves me wanting a little more, but still happy with the extra piece of the puzzle.