Prevalence of autism-spectrum conditions: UK school-based population study.

BACKGROUND Recent reports estimate the prevalence of autism-spectrum conditions in the UK to be 1%. AIMS To use different methods to estimate the prevalence of autism-spectrum conditions, including previously undiagnosed cases, in Cambridgeshire. METHOD We carried out a survey of autism-spectrum conditions using the Special Educational Needs (SEN) register. A diagnosis survey was distributed to participating schools to be handed out to parents of all children aged 5-9 years. The mainstream primary school population was screened for unknown cases. RESULTS The prevalence estimates generated from the SEN register and diagnosis survey were 94 per 10 000 and 99 per 10 000 respectively. A total of 11 children received a research diagnosis of an autism-spectrum condition following screening and assessment. The ratio of known:unknown cases is about 3:2 (following statistical weighting procedures). Taken together, we estimate the prevalence to be 157 per 10 000, including previously undiagnosed cases. CONCLUSIONS This study has implications for planning diagnostic, social and health services.