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.
The most recent prevalence estimates are based on data from 11 network sites in 11 states. The CDC plans to focus on 10 of these sites for future assessment. At six of the sites, clinicians plan to survey the records of children at both 4 and 8 years of age.