Is Rising Autism Prevalence Real or Displaces Other Mental Disorders?

In 19 70, the prevalence of autism in kids was zero point five. By 20 tenths, four decad later, almost 15 kids out of every thousand had atism. So that is almost a thirtyfold increase in atism. And what some people have been wondering was, well, is that increase really happening? Or is it that the atism was there all along, but in the past it had been diagnosed as something else?