Autism Is on the Rise (Or Is it?)

Correction (published Oct. 8, 2009): In the original article, the description of a study of autism in California misstated the percentage of new cases in that state that could be attributed to changing criteria for diagnoses. In the original, we said that 56 percent of the increase in autism cases could be explained by doctors diagnosing milder cases than they would have before, and that 24 percent came from doctors diagnosing cases in younger children, which meant that 20 percent of the new autism rate was unexplained. In actuality, 29 percent of the increase came from relaxed or changed diagnosis criteria and 4 percent came from cases being diagnosed in younger children, leaving 67 percent of the increase unexplained. The text has been updated to reflect this correction. NEWSWEEK regrets the error.

For years the autism community's most powerful public-relations weapon has been a striking statistic: an estimated 1 in 150 children have the diagnosis. Now it appears that estimate is actually too small. According to two new studies, the number of kids diagnosed with autism or a related disorder in the U.S. is closer to 1 in 100.

The new data has everyone who cares about autism abuzz. But, as with so many issues connected to the disorder, no one can quite agree on what it means.

One of the new studies, published in Pediatrics, is based on a survey of more than 78,000 parents. Researchers asked them if doctors had ever diagnosed any of their children with autism or a related disorder on the autism spectrum, such as Asperger syndrome. More than 1,400 of the parents said yes. If those numbers represent the population at large, that means 673,000 American kids likely have a form of autism.

Parent surveys often yield unreliable data because respondents may misremember or misunderstand what doctors have told them. But the Pediatrics study is backed up by a second, more reliable set of data collected by the Centers for Disease Control and Prevention (CDC). The full results aren't out yet, but on Friday, CDC researchers reported that one in 100 8-year-olds has been labeled with a disorder on the autism spectrum. That number is based on the same methods that yielded the original 1-in-150 statistic—so using CDC data alone, it's certain that autism diagnoses are on the rise.

That, however, is where the certainty stops. In the contentious autism community, two debates are constantly simmering: How many more children actually have autism now than had it in the past? And what are the underlying causes? The new numbers don't just fail to resolve either of these debates—they turn up the heat on both.

A rise in autism spectrum diagnoses doesn't necessarily mean a precisely corresponding rise in actual cases. Doctors may be inflating the numbers inadvertently by diagnosing the disorder more readily than they used to. Many doctors now diagnose autism and related disorders in children they might once have classified differently. Also, they may be more likely to give a child a diagnosis if they think that will help the child's parents obtain special-education services from public schools. Some are even willing to diagnose autism as a co-morbid condition in "people with clearly identifiable genetic disorders, such as Down syndrome—which is something that nobody would have dreamed of doing in the past," says Roy Grinker, a George Washington University anthropologist (and father of a child with autism) who believes the new numbers largely reflect an increase in diagnosis rather than actual illness.

At the same time, there's good evidence that more children actually are suffering from autism. In January, researchers at the University of California, Davis analyzed a seven- to eightfold increase in diagnoses in their state since 1990. Twenty-nine percent of that increase could be explained by doctors' diagnosing cases they might not have diagnosed before, says Irva Hertz-Picciotto, who led the study. Another four percent came from doctors diagnosing cases in younger children. But that still leaves 67 percent of the huge increase unexplained—and, says Hertz-Picciotto, that part is real.