Are Autism Rates Actually on the Rise, or Do We Just Define 'Autism' Differently Than We Used To?

Read: My Autism Doesn't Make Me a Robot

UPDATE 7/23: An earlier version of this article misstated the conclusions of the autism study—while the study indicates that a majority of the reported rise in autism rates can be explained by changes in diagnostic procedure, the study does not indicate that the rise can be solely attributed to this factor. This article has been edited throughout to correct this assumption.

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's rise can at least be partially explained by changes in how mental illness is diagnosed in children.

A team of researchers at Penn State University looked at 11 years worth of enrollment data from special-education programs, covering over 6 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. This implies that children who were more likely to be diagnosed with other intellectual disabilities in the past are more likely to be called "autistic" today, making it look like substantially more children have autism.

The process of diagnosing someone with autism is tricky, and the symptoms of autism can be diverse—behaviors 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."

According to that press release, "The researchers estimate that, for eight-year-olds, approximately 59 percent of the observed increase in autism is accounted for by reclassification, but by age 15 reclassification accounts for as much as 97 percent of the increase in autism."

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