Sure, we talk about an increase in awareness and changes in criteria and cultural perceptions. But why did this happen mostly in the 1990s? Lorna Wing coined the term Asperger's syndrome in 1981. The DSM-IV was published in 1994, years after the increasing trend in diagnosed cases had started. The trend accelerated after the DSM-IV publication, but there's no noticeable spike. I think there has to be an independent cultural phenomenon that drove changes in awareness and cultural perceptions.
I think the key to answering this question comes from parent experiences regarding how a child's diagnosis of autism came about. Usually it goes like this. The pediatrician tells the parents not to worry or gives an assessment completely unrelated to autism. The parents start to do their own research. Then they go to a hospital or find an specialist who is able to diagnose autism. My guess is that when parents visit a psychiatrist they typically already suspect the diagnosis of autism.
It is not far fetched to suppose that the internet has made a huge difference in providing parents the ability to carry out extensive research, and enhancing general awareness.
The internet began to take off shortly before the 1990s. At that time there was Usenet. There were mailing lists. It was more of an academic tool rather than a corporate one. Gopher was released in 1991 and begun to gain in popularity. By Q2 1994, the world wide web surpassed Gopher and that's when the internet really exploded.
What the hypothesis predicts
- Regions with higher internet penetration will tend to have a higher incidence of autism. (This would explain in part the link to degree of urbanization, with another factor being availability of specialists).
- In populations with no internet access whatsoever, autism will be virtually unheard of.
- At time of diagnosis, households with an autistic child are more likely to have internet service than households of a control group matched by age, even after social class is considered.
- Internet access correlates with reduced elapsed time from concern to diagnosis.