A large Danish study published in JAMA Psychiatry finds that children and teenagers diagnosed with ADHD or autism today are more similar to their peers than those diagnosed a decade ago. Researchers from ISGlobal and Aarhus University analyzed data from more than 2.1 million young people, comparing over 71,000 diagnosed individuals with more than 713,000 without either diagnosis.
The study tracked characteristics previously associated with ADHD and autism, such as premature birth, low birth weight, parental psychiatric history, and socioeconomic disadvantage. While these factors remained more common among diagnosed youth, the gaps steadily shrank over the study period. For example, low birth weight was linked to a 54% higher chance of diagnosis at the start of the period, but only a 17% higher chance by the end.
The authors suggest that increased awareness, better case identification, expanded access to evaluations, and changing thresholds for what is considered clinically impairing may all contribute. They caution that the findings do not mean the conditions are overdiagnosed or less severe, but that the population receiving diagnoses has changed. They also note that further research in other countries is needed to see if the pattern holds elsewhere.