The significant increase in autism diagnoses over the past two decades is attributable to a broadening of the disorder's definition rather than a rise in severe cases, according to a new study. The research, which analyzed autism diagnoses in Sweden between 2001 and 2020, found that the number of individuals diagnosed with autism who also have an intellectual disability has remained largely unchanged.
During this period, the proportion of autistic individuals with an intellectual disability (defined as an IQ below 70) dropped significantly, from 55.8% to 6.7%. Concurrently, the overall rate of children diagnosed with autism and an intellectual disability remained steady, at approximately 5.5 cases per 100,000 births in 2020.
The dramatic surge in overall autism diagnoses, an increase of roughly 800%, was driven by a 1,800% rise in diagnoses among individuals without intellectual disabilities. This suggests that many people diagnosed with autism in recent years would not have met the diagnostic criteria in the past.
"Autism today is assigned on significantly fewer symptoms than before," said Sebastian Lundström, one of the study's lead authors and a psychologist at the University of Gothenburg. "We have also shown that even though the diagnosis increases, the symptoms constituting autism in the population do not increase."
Lundström described the shift, noting that the