Annex 2: Prevalence and incidence
The prevalence estimates in the Public Health Institute of Scotland's ( PHIS) ASD Needs Assessment Report suggested 60 in every 10,000 people are affected by ASD. More recent studies suggest that a rate of around 1 in 100 is currently the best estimate of the prevalence in children and adults.  
Diagnosis for school age children is vastly improved both in its sophistication and in its consistency. This has led to benefits for some adults in the extended family of those recently diagnosed children whereby they have come forward to ask for their own diagnosis as they recognise similar behavioural patterns within themselves. There is no one single explanation of why more people appear to be diagnosed with the condition. It is probable that a mix of factors is coming into play including increasing public and professional awareness, improved diagnosis, wider diagnostic criteria or a combination of all the above.
As part of its acceptance of the PHIS recommendations, the then Scottish Executive undertook an audit of services for people with ASD in 2004  . Its remit was to provide information for service commissioners on the best available knowledge about ASD and current service provision in Scotland, and guidance on how these services might better meet the needs of both children and adults with ASD in the future. The intention was to assess the extent to which national prevalence rates could be regarded as a sound basis on which to plan services. It was also the first time that social and health care planners for both children and adult services attempted to quantify the incidence of ASD in their locality. Whilst the ultimate analysis carried a number of reservations about the reliability of the findings, acknowledging its patchiness and the likelihood of underestimation, it did provide a much clearer picture than had existed up until that point. It meant that many planners did take the opportunity to discuss the findings together and to plan appropriate interventions at local level.
The overall picture that emerged was that 35 children per 10,000 were diagnosed with ASD, making a total 3,400 children and young people. Within this, the highest rate was for the 5-10 age group where there were 49 children diagnosed per 10,000 population. Incidence figures have varied across Health Boards from 16 in Forth Valley to 102 in Highland and 299 in Orkney. For the 11-15 age group, there were 27 children and young people diagnosed per 10,000 population which drops to 16 per 10,000 population for the 16-18 age group.
The higher rates for the 5-10 and preschool age groups was thought to have been due to a combination of better reporting procedures and improved diagnosis in recent years. The rate per 10,000 population for preschool children at 42 was less than the rate for 5-10 year olds. It could have been expected that the pre-school data should have been of equal or better quality than the 5-10 age group because of improved reports but much diagnosis takes place after the age of 3 because the behaviours associated with the condition may not be displayed before then. Other significant findings were that 20% of children with ASD were reported as having learning disabilities with two thirds of diagnosed primary school children attending mainstream schools. Around one third of children with ASD were specifically diagnosed with Asperger's syndrome.
Moving to adults, 645 adults were identified in the audit, 1 in 7 of whom was described as having Asperger's. The data here was less robust. Eight of the 15 NHS Boards were able to provide complete information but 4 could not do so. NHS Lothian conducted a file review so that its data was possibly the most accurate. Given these limitations, we see that 24% of people were in the 18-24 bracket, 63% were aged 25-29 and 12% were over 50 years of age. The rate was highest for the 18-24 age group where for Scotland there were 5.1 people diagnosed per 10,000 population. This changes to 3.2 for the 25-49 age group and again to 0.6 for the 50 plus age group. As before, these lower rates probably reflect a combination of better reporting procedures and improved diagnosis over the years. As with the children's data, the rates of diagnosis vary considerably between NHS Board areas from 0.8 per 10,000 population in Lanarkshire to 8.7 people diagnosed per 10,000 population in Orkney.
Overall, more than half (55%) of the adults with ASD that were known to partnerships also had learning disabilities. In addition, nearly one third of these adults had other behavioural or biomedical conditions, 10% had both a learning disability and a physical impairment and 3% had mental health problems.
Since the time the survey was conducted, some authorities have built on this data to continue local planning. The Scottish Government now collects data on the number of school children with autism. The Pupils in Scotland 2010 publication and the Independent School census (September 2008) record the number of children for reason of support of autism spectrum disorder as being 6,506 which is closer to 1 in 100.
The prevalence figures outlined in Table 2 are estimates of the total number of people with autism spectrum disorder by local authority area, based on the prevalence rate of 90 in 10,000 people from the Office of National Statistics survey of the mental health of children and young people in Britain (2005). The ratio of males to females was found to be 4:1. Not all of this population will need formal community care services. Many will need life time support. However, it is clear from the figures that wider community services, such as housing, transport, sport and leisure, should be taking account of the range of needs of this population.
|Location||Population||Estimated||0 to 4||5 to 9||10 to 14||15 to 19||20 to 29||30 to 65|
|(Caps -city status)||2006||90/10,000||M||F||Total||M||F||Total||M||F||Total||M||F||Total||M||F||Total||M||F||Total|
|Argyll & Bute||91390||823||40||10||50||42||10||52||43||11||54||42||11||53||87||22||109||307||77||384|
|Dumfries & Galloway||148030||1332||64||16||81||68||17||85||69||17||86||68||17||85||141||35||176||498||124||622|
|Perth & Kinross||140190||1262||61||15||76||64||16||80||65||16||81||65||16||81||133||33||166||471||118||589|
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