ASD prevalence has increased 3.5-fold in Stockholm between 2001 and 2011 [@idring2015]. Why?

The increase in ASD prevalence is likely contributed to by extrinsic factors such as increased awareness and diagnostics. [@idring2015]

Lundström2015 - Autism phenotype versus registered diagnosis in Swedish children, prevalence trends over 10 years in general population samples:

The prevalence of the autism symptom phenotype has remained stable in children in Sweden while the official prevalence for registered, clinically diagnosed, autism spectrum disorder has increased substantially. This suggests that administrative changes, affecting the registered prevalence, rather than secular factors affecting the pathogenesis, are important for the increase in reported prevalence of autism spectrum disorder.

Now in 2022, Sweden is a global outlier together with the US, UK and Japan in the number of ASD cases (see Figure in [@solmi2022]).