Estimating the Prevalence of Autism Spectrum Conditions in Adults: Extending the 2007 Adult Psychiatric Morbidity Survey
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 this into account, at 1.1 percent nationally is slightly higher than the previous estimate of 1.0 percent 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.
§ The overall prevalence of autism, combining data from the APMS 2007 and learning disability study, was 1.1 per cent (95 per cent confidence interval 0.3 per cent to 1.9 per cent). The prevalence of autism was higher in men (2.0 per cent) than women (0.3 per cent).
§ In the learning disability study it was found that the prevalence of autism increased with greater severity of learning disability/lower verbal IQ.
§ Among adults with learning disabilities living in private households whose learning disability was sufficiently severe that they could not have taken part in the APMS 2007, the prevalence of autism was 35.4 per cent (95 per cent confidence interval 24.7 per cent to 46.2 per cent). Among adults with mild or severe learning disabilities living in communal care establishments, the prevalence of autism was 31.0 per cent (95 per cent confidence interval 23.9 per cent to 38.0 per cent).
§ Sex differences were less marked in adults with learning disabilities compared with the rest of the general population (APMS 2007).
§ The estimated prevalence of autism changed very little when the data were re-analysed to take into account that the prevalence of autism might be higher or lower in other settings, such as prisons or defence establishments. Using assumptions based on different scenarios to take these into account, the overall prevalence of autism was estimated at between 1.1 per cent and 1.2 per cent.