I predict that the prevalence of autism spectrum disorders is done increasing because it has all come from better diagnosis. The autism rate in children has now reached one in 88; the autism rate in adults is estimated at one in 86. We just went within my error bars.
There are two things that I think could confuse the issue. The first is that the DSM-V will come out soon. If, following the DSM-V, diagnosticians continue exactly what they're currently doing, except that they diagnose all autism spectrum disorders as autistic disorder (which will not affect the one in 88 statistic because Asperger's and PDD-NOS have always been part of it), then the prevalence rate has stopped increasing. If, following the DSM-V, diagnosticians do what it tells them, the prevalence rate will decrease, with the loss coming from people with PDD-NOS who have communication or language difficulties and one of the other two points in the triad of impairments.
The second is that the adult rate may be lower than the childhood rate because of the existence of people who are diagnosable as children but not as adults because of learned coping skills. If that's true, the rate may continue to increase.
I will consider myself right if it reaches one in 84, slightly surprised at one in 80 (I'll assume I underestimated the number of people diagnosable only as children), shaken and looking for explanations at one in 75 and outright wrong (I will abandon the theory and concede defeat) if the prevalence reaches one in 70 without some really significant evidence of overdiagnosis.
I also allocate some probability mass to the idea that the prevalence rate will decrease. I don't predict a huge decrease with great likelihood, but if I do see one, I will update on my beliefs about diagnosticians and watch who is and isn't getting diagnosed in the next youngest cohort. If the DSM-V causes such a drop, I would expect it to more likely be sudden as doctors adopt changes after the DSM-V comes out, but it could be slow and steady if older doctors do as they were already doing and younger doctors act differently. Those cases could be distinguished by looking at diagnoses made by older doctors and newer ones and comparing them.
I note that while I do not predict a huge drop with great probability, mine is the only theory which would explain any drop at all.
I predict that if there is a drop, John Best will claim that "lying neurodiverse psychopaths" are somehow responsible and that it harms "actual autistics" and their families. Note that I assign only small probability to the actual phrases given. For instance, he may suggest "real autistics" or "families actually affected by real autism" or any number of things. ("Psychopaths" will be in there somewhere as a description of people who do not want a cure for autism. If he doesn't call them liars in his blog post, they will be called liars somewhere in the comments.) If I am wrong, the most likely other possibility is that he is triumphant and believes that his supporters are "getting the message out" and parents are not vaccinating anymore. My model of reality takes a hit if John Best ever claims that new and surprising evidence does not support his ideas about autism. This does not apply to everyone who is against vaccines. It only applies to him.
(Trivial prediction: you will get upset if you read his blogs. Don't go looking for them unless your utility function values becoming upset over false claims.)
If the autism rate is stable, this is evidence that it has been stable for a long time (I believe this because the increasing rate has been used as evidence that it did not exist before the last century and that it is environmentally caused) and if it has been stable for a long time, this is evidence against it being caused by vaccines, because that would have caused the prevalence to increase.
Please spread this around as much as possible. I am predicting ahead of time that: The autism rate does not go above one in eighty, probably stays stable in the high-to-mid eighties and may decrease. I admit that I was wrong if it reaches one in seventy. Please help: I want this well-known. I want people to know I made the prediction before we see the evidence. Sharing a link to this would be a quick and easy way to increase average utility and expose people to the idea of falsifiable ideas that make predictions about what they will and won't see.