Autism - a question of diagnosis?

In the U.S. the Centre for Disease Control estimates that rates of autism have gone up by 60% for boys since 2002 and by 48% for girls. But do these increases reflect a genuine rise in the number of children with the condition or simply the fact that more children are being diagnosed with it? Matthew Maenner a Ph.D. student at the University of Wisconsin-Madison studied the levels of autism in Wisconsin. He found that the rate rose from five to nine cases per 1,000 children over a seven-year period. At the start of the study individual schools varied widely in the number of children diagnosed with autism with the highest-diagnosing schools having a rate 24 times greater than the lowest-diagnosing ones. However, over time, the gap narrowed and by the end of the study the highest-diagnosing schools had a rate only twice that of the lowest-diagnosing ones. The schools who had around a 1% rate of autism at the start of the study showed little change in their rate of diagnosis suggesting that it was more-frequent diagnosis in the lower-diagnosing shcools rather than a genuine increase in the condition that lay behind the increased rates of the disease.