Has our definition of autism changed over the years?
How people think about and diagnose autism has changed substantially since the diagnosis was first introduced nearly 75 years ago. In 1943, Leo Kanner firstcoined the term ‘infantile autism’ to describe children who seemed socially isolated and withdrawn.
In 1966, researchers estimated that about 1 in 2,500 children had autism, according to criteria derived from Kanner’s description. This and other early estimates of prevalence probably focused on children at the severe end of the spectrum and missed those with subtler features.
Autism didn’t make its debut in the DSM until 1980. In 1987, a new edition expanded the criteria by allowing a diagnosis even if symptoms became apparent after 30 months of age. To garner a diagnosis, a child needed to meet 8 of 16 criteria, rather than all 6 of the previous items. These changes may have caused the condition’s prevalence to tick above 1 in 1,400.
Then, in 1991, the U.S. Department of Education ruled that a diagnosis of autism qualifies a child for special education services. Before this time, many children with autism may instead have been listed as having intellectual disability. The change may have encouraged families to get a diagnosis of autism for their child. The number of children who have both a diagnosis of autism and intellectual disability has also risen steadily over the years.
In 1994, the fourth edition of the DSM broadened the definition of autism even further, by including Asperger syndrome on the milder end of the spectrum. The current version, the DSM-5, was released in 2013, and collapsed autism, Asperger syndrome and pervasive developmental disorder-not otherwise specified into a single diagnosis.
The most recent CDC estimate of autism prevalence is based on the fourth edition of the DSM. Future estimates will be based on DSM-5 criteria—which may lower autism rates.