It used to be that ten years ago, for every 156 eight-year-olds, one would have autism. In 2004, that figure had risen to 1 in 125. By 2006, 1 in 110 children had it, and according to data released this March by the Centers for Disease Control, 1 in every 88 kids in America had the disorder in 2008. And that's just the national average. In some select places, such as Utah and New Jersey, the rate approaches an alarming 1 in 47. The CDC report paints a picture of a rapidly expanding autistic population. But it doesn't tell us why so many more children are being diagnosed with the developmental disorder now than before. One obvious possibility is that the rate of autism really is increasing -- whether through factors in our surroundings that we can control or thanks to genetic factors we can't. But it could also be that the rise in autism diagnoses has nothing to do with the actual disease so much as the way we talk about it. As Dorothy Bishop, a professor in developmental psychology at Oxford, notes on her blog, what we're seeing may just be a matter of "diagnostic substitution." "The basic idea," she writes, "is that children who would previously have received another diagnosis or no diagnosis are now being identified with autism spectrum disorder (ASD)."
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