This report presents a new estimate of the prevalence of autism among adults aged 18 years and over. This was derived using data from the 2007 Adult Psychiatric Morbidity Survey (APMS 2007) in combination with data from a new study of the prevalence of autism among adults with learning disabilities, who are a key group to study because they could not take part in the APMS 2007 and have been found to have an increased risk of autism.
The study was based on adults with learning disabilities living in private households and communal care establishments in Leicestershire, Lambeth and Sheffield. Whilst the study comprised a relatively small sample with limited geographical coverage and did not include the institutional population, it did include two non-mutually exclusive populations (people in communal care establishments and people with learning disabilities) which were not covered by the APMS 2007.
The study demonstrates that autism is common among people with a learning disability and, in taking these into account, at 1.1 per cent nationally is slightly higher than the previous estimate of 1.0 per cent in the APMS 2007. Sensitivity analysis showed that the estimates for national prevalence produced by this study were relatively insensitive to inaccuracies caused by the limitations.