A decade of rising diagnosis rates for attention deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) has prompted significant debate among clinicians, parents, and policymakers. While much of the scientific discourse has focused on whether the actual prevalence of these neurodevelopmental conditions is surging, new research suggests that the answer may be far more nuanced. A study led by the Barcelona Institute for Global Health (ISGlobal)—a center supported by the "la Caixa" Foundation—and Aarhus University indicates that the fundamental profile of the individuals receiving these diagnoses has undergone a profound transformation.
According to the study, which was recently published in the journal JAMA Psychiatry, young people diagnosed with ADHD or ASD in Denmark today bear a closer resemblance to the general population than those diagnosed just ten years ago. This suggests that the marked increase in clinical diagnoses may be driven, at least in part, by changes in the identification process and the population being assessed, rather than solely by a shift in the biological likelihood of developing these conditions.
Tracking the Evolution of ADHD and Autism Diagnoses
For years, epidemiological research has consistently pointed to a specific cluster of characteristics that appear more frequently in individuals with ADHD and ASD compared to the general population. These established risk markers include factors such as preterm birth, low birth weight, parental history of psychiatric conditions, lower levels of parental education, and limited household income. Furthermore, individuals who eventually received a diagnosis often demonstrated a history of higher utilization of healthcare services—including visits to general practitioners and specialists—well before the formal diagnostic process was completed.
As diagnosis rates for ADHD and ASD began to climb internationally, researchers at ISGlobal and Aarhus University sought to determine whether the "typical" profile of a patient had remained stable or if it had shifted alongside the rising numbers. To explore this, the team conducted a massive, longitudinal analysis using data from over 2.1 million children and adolescents residing in Denmark. The scope of the study allowed for a rigorous comparison: researchers examined more than 71,000 young people diagnosed with either ADHD or ASD between 2012 and 2022 and contrasted their profiles against a control group of more than 713,000 individuals who had never received such a diagnosis.
Narrowing Differences Over a Decade
The data revealed a clear, measurable trend: while individuals diagnosed with ADHD or ASD were still statistically more likely to possess the traditionally linked risk factors than their peers, the strength of these associations has significantly waned over the last ten years. The gap between those diagnosed with neurodevelopmental conditions and the general population is closing.
One of the most striking examples of this phenomenon involves birth weight. At the outset of the study period, the data showed that children born with a low birth weight were 54% more likely to receive an ADHD or ASD diagnosis compared to those born at a normal weight. By the conclusion of the study in 2022, that disparity had plummeted to just 17%. The researchers observed similar, comparable declines in the associations between neurodevelopmental diagnoses and other previously strong indicators, including premature birth and various socioeconomic disadvantages.
Magnus Elias Tarp, a PhD student at Aarhus University and the lead author of the study, emphasizes that these results should not be interpreted as a dismissal of known risk factors. Instead, the research highlights a changing landscape of diagnostic criteria and outreach. "The key message is not that these risk factors are no longer important," Tarp explains. "What we found is that people diagnosed in recent years resemble the general population more closely than those who received the same diagnoses a decade ago."
A New Perspective on Rising Diagnosis Rates
The findings provide a fresh lens through which to view the current surge in ADHD and ASD diagnoses. Historically, much of the research in this field has been framed by a binary question: are we seeing a genuine increase in the incidence of these conditions, or is this a result of diagnostic inflation? By analyzing whether the population receiving the diagnoses has changed, the researchers have introduced a third, critical possibility.
Several external developments may be contributing to this shift. Increased public awareness has likely encouraged more families to seek evaluations for children who might have been overlooked in the past. Simultaneously, advancements in the effectiveness of healthcare and education systems in identifying neurodivergent traits have likely expanded the net, allowing for earlier or more frequent detection. Furthermore, access to formal diagnostic evaluations has broadened, and the thresholds at which certain behaviors are deemed "clinically impairing" may have shifted as clinical understanding of the spectrum has evolved.
While the current study cannot quantify the precise contribution of each of these factors, the researchers believe the findings are transformative for how we interpret clinical data. Oleguer Plana-Ripoll, a researcher at ISGlobal and Aarhus University and the senior author of the study, cautions against making simplistic conclusions about the prevalence of these conditions. "Our findings help us better understand why ADHD and autism diagnoses have increased so markedly in recent years," says Plana-Ripoll. "They do not show that these conditions are being overdiagnosed or that they have become less severe. Rather, they indicate that the population receiving these diagnoses has changed over time, and this needs to be taken into account when interpreting current trends."
Plana-Ripoll also notes the necessity of international context. Because the study was conducted within the Danish healthcare system, which provides universal, data-rich access to services, further research in other countries will be essential to determine if this pattern of "normalization" in diagnosis profiles is a global phenomenon or specific to certain healthcare environments.
Implications for Healthcare and Policy
The implications of this research extend far beyond the academic community. If the population of individuals receiving a diagnosis is becoming more representative of the general public, it necessitates a significant pivot in how public services are planned and delivered.
Healthcare providers, educators, and social service agencies rely on the profiles of the populations they serve to allocate resources effectively. If the profile of an "average" ADHD or autistic patient is no longer defined by the high-risk, low-socioeconomic markers of the past, then the types of support, outreach, and clinical interventions required may also need to change. Planning for these services must account for a more diverse demographic than was previously the focus of clinical attention.
Moreover, these findings carry significant weight for researchers studying the long-term outcomes of people with ADHD or ASD. In recent years, studies have often reported improvements in outcomes for these populations, leading to debates about whether interventions have become more effective or if the conditions themselves are manifesting differently. This new study suggests a "selection bias" of sorts: some of the apparent improvements in outcomes may actually be attributed to the changing characteristics of the individuals receiving the diagnoses. If the individuals currently entering the diagnostic pool have different baseline risks or protective factors than those from a decade ago, it is perhaps inevitable that their long-term trajectories would look different.
As the scientific community continues to grapple with the rising numbers of neurodevelopmental diagnoses, the research from ISGlobal and Aarhus University provides a vital reminder: data regarding health trends must always be viewed in the context of the people behind the numbers. By recognizing that the population receiving diagnoses is becoming more reflective of society as a whole, stakeholders can better refine their approach to support, ensuring that diagnostic efforts remain focused on meeting the needs of a diverse and changing community.
