Since it was discovered in the mid-1900s, autism has increased exponentially. In 1974, autism affected a scant one in 5,000 children in the United States. By 2010, that number was one in 68, or about 1.5 percent of children in the United States. Between 2000 and 2010 alone, the rate of autism increased threefold.
This "autism epidemic" has been falsely explained by things like circumcision and vaccines. Some parents are so afraid of autism that they've refused to vaccinate their kids; others have tried to "cure" their autistic kids through extreme measures like bleach enemas. But according to a study published today in the American Journal of Medical Genetics, autism isn't actually on the rise. It just looks that way because of the way autism is diagnosed.
A team of researchers at Penn State University looked at 11 years worth of enrollment data from special-education programs, covering over six million children. In that time frame, researchers found no increase in special-ed enrollment—just a shift in the number of students who had been diagnosed with autism. Children who were more likely to be classified with other intellectual disabilities in the past are more likely to be called "autistic" today, making it look like more children have autism.
Autism diagnosis is tricky, since it's based entirely on behavior. The symptoms of autism can be diverse and generic—things like arranging objects in linear patterns or performing repetitive behaviors are considered symptoms. When the condition was first named by Leo Kanner in 1943 (the same dude who invented the term "refrigerator mothers"), autism was considered rare and specific. Today, autism is known to exist "on a spectrum," appearing in many different forms and with much greater variability.
This can make it easy to conflate symptoms of other intellectual disorders with autism, according to Santhosh Girirajan, the leader of the research team. In a press release, Girirajan explained, "When individuals carrying classically-defined genetic syndromes were evaluated for features of autism, a high frequency of autism was observed, even among disorders not previously associated with autism, suggesting that the tools for diagnosing autism lose specificity when applied to individuals severely affected by other genetic syndromes."
In other words: The increase in autism is because of how the condition is diagnosed, not how the condition itself is caused.
For younger kids, the researchers found that about 59 percent of the increase in autism was accounted for by reclassification from other neurological disorders. By age 15, reclassification accounted for 97 percent of the increase in autism.
This is the first study to show direct evidence against the idea that autism is on the rise. It's not something in the water, or in the vaccines we give to children, but rather the way doctors handle autism diagnoses that's responsible for the increase in autistic children.
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