Most of the increase can easily be explained by the change in diagnostic criteria. The rest is pretty well covered by the fact that autistic kids do not in fact magically disappear when they grow up leading to the uncomfortable realization that adults can in fact be autistic. Well that and the fact that people who aren’t white exist, and I suppose women are real too.
We went from only middle to upper class white male children being able to have autism to black grandmothers* being able to be diagnosed and people wonder why more people end up with diagnosis. These studies are staring off on a false premise at best and often dive headlong into eugenics.
It is worth noting that one couldn’t get diagnosed with both ADHD and autism until 2013, and since 50-70% of people with ASD also have ADHD, that would increase the numbers further.
ADHD has a similar story, but I think I’ve rambled enough for now.
*(if she is wealthy enough)
These days we have been going by the rule:
The people I play with are far too inconsistent and we have to take what we can get. Complicating things too much is just another barrier that we don’t need. We do have a decent sized group with a couple of reliable players, so this is probably easier to do with this group than with a smaller one.
Note: We are all pushing 50 and are pretty busy with work and family, which is a big contribution to the flakiness.