Over the last 30 years the number of diagnosed cases has increased from 0.4-0.5 to 4.0 per 1000 for autistic disorder and from 2 to 7.7-9.9 per 1000 for autism spectrum disorders which is largely attributable to broadening

diagnostic criteria,

younger age at diagnosis and improved case ascertainment.

Autism spectrum disorders are increasingly being recognised as a major public health issue.