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Definition and prevalence of autism spectrum disorder
Within this document the term "autism spectrum disorder" ( ASD) is used as it is the most common term in use today. Some people may refer to autism spectrum conditions, however autism spectrum disorder is used and recognised in current practice when considering diagnostic issues. In this sense it should be seen as relating to experiences outwith the normal sequence rather than a pejorative term implying "defect". This guidance aims to promote the development of services for all people on the autism spectrum, this includes higher functioning people with a diagnosis of autism and those with Asperger Syndrome, based on individual need and not on the basis of a specific diagnosed condition.
Autism and its related conditions are defined as "Pervasive Developmental Disorders" as the typical features appear during an individual's period of growth and development. These conditions are assumed to be life-long but there is considerable variation in both how individuals present over their own lifetime and in comparison to one another. It is therefore important to consistently identify and assess an individual's experiences and this is usually provided as a formal diagnosis.
A formal diagnosis should not be about just attaching a "label" to a person. The national Diagnostic Guidelines in Annex A highlight that this should be a participative process that consolidates knowledge and understanding of an individual's needs, and generates options for change and future support.
The SIGN Guideline describes the two internationally accepted diagnostic classification systems: ICD-10 and DSM-IV. The criteria in both are based on the Triad of Impairments which means that an individual demonstrates problems in socialisation skills, abnormal language and communication development, and rigidity of thought and behaviour.
Prevalence studies at the time of publication of the PHIS Report resulted in estimates of 7714 children under 19 in Scotland. More recent studies suggest that a rate of around 1 in 100 is currently the best estimate of the prevalence in children, suggesting over 50,000 people in Scotland 4. Within this population possibly up to 40% may be considered to have a diagnosed learning disability but many of the others will have difficulties in aspects of learning and acquiring information even though they may possess very superior cognitive levels. The focus on intellectual functioning is due to the current diagnostic standards where typically, individuals with a learning disability have been diagnosed with "Autism" while more able people have been described as fulfilling the criteria for "Asperger Syndrome".
Prevalence studies have not been carried out on adults and would be difficult to do well. Information from services across Scotland suggests that an increasing number of more able adults are seeking and receiving a primary diagnosis. It is also evident that in many cases this is sought following an individual's increased awareness of autism spectrum disorder as a consequence of a diagnosis given to a school-age relative.
The economic consequences of autism in the UK have been outlined in a recent report which can be accessed at the following link. http://www.learningdisabilities.org.uk/publications?EntryId=28948 .
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