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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.
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Policy changes may have also played a role. In 2006, the American Academy of Pediatrics recommended screening all children for autism during routine pediatrician visits at 18 and 24 months of age. This move may have led to diagnoses for children who would otherwise have slipped under the radar.
The prevalence of autism in the United States has risen steadily since researchers first began tracking it in 2000. The rise in the rate has sparked fears of an autism ‘epidemic.’ But experts say the bulk of the increase stems from a growing awareness of autism and changes to the condition’s diagnostic criteria.
Here’s how researchers track autism’s prevalence and explain its apparent rise.
How do clinicians diagnose autism?
There is no blood test, brain scan or any other objective test that can diagnose autism—although researchers are actively trying to develop such tests. Clinicians rely on observations of a person’s behavior to diagnose the condition.
In the U.S., the criteria for diagnosing autism are laid out in the “Diagnostic and Statistical Manual of Mental Disorders” (DSM). The criteria are problems with social communication and interactions, and restricted interests or repetitive behaviors. Both of these ‘core’ features must be present in early development.
What is the prevalence of autism in the U.S.?
The Centers for Disease Control and Prevention (CDC) estimates that 1 in 68children in the U.S. have autism. The prevalence is 1 in 42 for boys and 1 in 189 for girls. These rates yield a gender ratio of about five boys for every girl.
How does the CDC arrive at this number?
CDC researchers collect health and school records for 8-year-old children who live in select U.S. counties. These researchers are part of the Autism and Developmental Disabilities Monitoring Network, which the CDC set up in 2000 to estimate autism prevalence.
Every two years, trained clinicians scan the records for signs of autism features, such as social problems or repetitive behaviors. They focus on 8-year-olds because most children are enrolled in school and have had routine health assessments by that age2. They then decide whether each child meets the criteria for autism, even if the child does not have a diagnosis, and extrapolate the results to all children in the state.
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