I explained about the AQ50 being a screening tool that is designed to deliver false positives in order to minimise false negatives. So we expect some NT kids to score over the threshold, that's an acceptable trade-off.
There's a downloadable PDF of the whole paper that gives a by-sex breakdown of the autistic kid's scores in a huge table on the page marked 348. The graphic makes it easier to see the two clear peaks but doesn't allow for precise analysis. A bar chart would have been more appropriate for representing this data.
Looking at the table, the lowest AQ50 score that any autistic children achieved was 24. The highest AQ50 score achieved by any of the control group was 29. The total proportion of kids by sex from each group who scored from 24 to 29 inclusive was
- Asperger boys: 10.2%
- Autism boys: 6.3%
- Control boys: 24%
- Autism girls: 12.5%
- Asperger girls: 0%
So not 50% overlap, at all: an overlap in AQ50 score between the highest-scoring 24% of control boys and the lowest-scoring 10% of Asperger boys and the lowest-scoring 6.3% of autistic boys, in a screening tool that's designed to quickly rule out autism in those who almost certainly don't have it and so only checks for the most noticeable and common traits. A more thorough assessment of those 24% of control boys might reveal any of the following:
- A missed autism diagnosis.
- A missed diagnosis for another neurodivergent condition, such as ADHD.
- Failure to detect trauma from ACEs that manifests as coping strategies that mimic autism.
The data from that paper demonstrates that there is very little overlap in the prevalence of noticable and common traits between autistic people and neurotypical people and very few people have a small amount of traits or only manifest traits mildly, which is the point I am making to counter the "we're all on spectrum" myth.