It would be interesting to try and repair the data some how. Surely there are stats on the number of retards etc. that they now just classify as autistic. In addition to reclassification, there is also a wide broadening of diagnosis, mainly to increase the potential market base for pharmaceuticals. This happens with lots of diseases that are "increasing rapidly". Basically, the underlying data is corrupted and can't really be used for any meaningful analysis because the scientists who were collecting it sold out in their ethical obligations to collect quality data. That being said, the rate of "autistic screeching" level autism does seem to be markedly rising over the last 40-50 years.