Are there more people with autism, or more people diagnosed with autism?

The LA Times has a really interesting and well-done four-part series on autism. The central question: Does the increase in people diagnosed with autism represent an actual increase in prevalence of autism, or an increase in diagnosis and awareness?

The evidence presented in the Times story seems to suggest the latter. In the first part of the series, writer Alan Zarembo looks at the social change surrounding autism. Over the last 20 years, not only has the diagnosis changed and become broader, but parents have become more aware that autism is a thing, and financial incentives have appeared that make parents more inclined to fight for an autism diagnosis for their child—even when experts aren't sure that's actually what's going on with that particular child.

If that part of the story makes you sort of hostile toward the parents, consider the fourth part of the series, where Zarembo looks at people who, after years of struggle, are getting diagnosed with autism as adults. It's a nuanced view. Yes, there are some kids diagnosed with autism today who don't actually fit the diagnosis. But, in the past, a lot of people didn't get diagnosed at all. Behavioral therapies, educational aides, even the simple knowledge that there are other people who think the way they do—all these things could have improved those people's lives. So, yeah, social constructs have changed who we diagnose with autism. But maybe that's actually a good thing? Here's a couple particularly powerful excerpts:

From the first part of the series:

Irva Hertz-Picciotto, an epidemiologist at UC Davis, suspects that environmental triggers such as exposure to chemicals during pregnancy play a role. In a 2009 study, she started with a tantalizing lead — several autism clusters, mostly in Southern California, that her team had identified from disability and birth records.

But the hot spots could not be linked to chemical plants, waste dumps or any other obvious environmental hazards. Instead, the cases were concentrated in places where parents were highly educated and had easy access to treatment.

...a more surprising pattern that existed across the state: Rich or poor, children living near somebody with autism were more likely to have the diagnosis themselves. Living within 250 meters boosted the chances by 42%, compared to living between 500 and 1,000 meters away. The reason, analysis suggested, was simple: People talk.

And from the fourth part of the series:

The only study to look for autistic adults in a national population was conducted in Britain and published in 2009. Investigators interviewed 7,461 adults selected as a representative sample of the country and conducted 618 intensive evaluations.

The conclusion: 1% of people living in British households had some form of autism, roughly the same rate that the U.S. Centers for Disease Control and Prevention estimates for children in America today.

The British study found it didn't matter whether the adults were in their 20s or their 80s. The rate of autism was the same for both groups.

“That would seem to imply the incidence has not changed very much,” said Dr. Terry Brugha, a professor of psychiatry at the University of Leicester who led the study. He added that the findings were not conclusive and more research is needed.