How many people in the UK have autism?
Around 700,000 people may have autism, or more than 1 in 100 in the population.
There is no register or exact count kept. Any information about the possible number of people with autism in the community must be based on epidemiological surveys (ie studies of distinct and identifiable populations).
The latest prevalence studies of autism indicate that 1.1% of the population in the UK may have autism. This means that over 695,000 people in the UK may have autism, an estimate derived from the 1.1% prevalence rate applied to the 2011 UK census figures.
The prevalence rate is based on two relatively recent studies, one of children and the other of adults. The prevalence study of children, (Baird G. et al., 2006) looked at a population in the South Thames area. The study of adults was published in two parts, Brugha et al (2009), and The NHS Information Centre, Community and Mental Health Team, Brugha et al (2012). This is the only known prevalence study to have been done of an adult population.
Autism and learning disabilities
What proportion of people with autism have a learning disability?
Between 44% - 52% of people with autism may have a learning disability.
Between 48% - 56% of people with autism do not have a learning disability.
Research findings on the proportion of people with autism spectrum disorders who also have learning disabilities (IQ less than 70) vary considerably as they are affected by the method of case finding and the sample size.
Fombonne et al (2011), in their research review of 14 prevalence studies that mentioned IQ, found a range of 30% to 85.3%, with a mean of 56.1%, of people without learning disabilities, p. 99.
Emerson and Baines (2010) in their meta-analysis of prevalence studies found a range of people with learning disabilities and autism from 15% to 84%, with a mean of 52.6%.
Explanation of why these findings are so variable and the reliability of the figures can be found in both Emerson and Baines (2010) and in Fombonne et al (2011).
What proportion of people with a learning disability have autism?
Around a third of people with a learning disability may also have autism.
Around a third of people who have learning disabilities (IQ less than 70) also have autism, according to research published by Emerson and Baines in 2010. The adult prevalence study, The NHS Information Centre, Community and Mental Health Team, Brugha et al.(2012), found between 31% and 35.4% of people with a learning disability have autism.
Autism and gender
How many males compared to females are diagnosed with autism?
Five times as many males as females are diagnosed with autism.
The proportion of males as opposed to females diagnosed with autism varies across studies, but always shows a greater proportion of males. Fombonne at al (2011) found a mean of 5.5 males to 1 female in their research review.
Baird et al (2006) found a male to female ratio of 3.3:1 for the whole spectrum in their sample. The Adult Psychiatric Morbidity Survey looked at people in private households, and found a prevalence rate of 1.8% male compared with 0.2% female, (Brugha et al, 2009). However, when they extended the study to include those people with learning disabilities who had been unable to take part in the APMS in 2007 and those in communal residential settings, they found that the rates for females were much closer to those of the males in the learning disabled population, (The NHS Information Centre, Community and Mental Health Team, Brugha et al., 2012).
Note that autism spectrum disorders are under-diagnosed in females, and therefore the male to female ratio of those who have autism may be closer than is indicated by the figure of 5:1. The under recognition of autism spectrum disorders in females is discussed in Gould and Ashton-Smith (2011).
An historical outline of epidemiological studies of autism
It is more than 50 years since Leo Kanner first described his classic autistic syndrome. Since then, the results of research and clinical work have led to the broadening of the concept of autistic disorders. In consequence, estimates of prevalence have increased considerably. This process has occurred in stages, the start of each of which can be linked to particular studies. The history is summarised and the most up-to-date figures are given below and in the table overleaf.
The specific pattern of abnormal behaviour first described by Leo Kanner is also known as 'early infantile autism'. Kanner made no estimate of the possible numbers of people with this condition but he thought that it was rare (Kanner, 1943).
Over 20 years later, Victor Lotter published the first results of an epidemiological study of children with the behaviour pattern described by Kanner in the former county of Middlesex, which gave an overall prevalence rate of 4.5 per 10,000 children (Lotter, 1966).
The triad of impairments in children with learning disabilities
In 1979 Lorna Wing and Judith Gould examined the prevalence of autism, as defined by Leo Kanner, among children known to have special needs in the former London Borough of Camberwell. They found a prevalence in those with IQ under 70 of nearly 5 per 10,000 for this syndrome, closely similar to the rate found by Lotter. However, as well as looking at children with Kanner autism, Wing and Gould also identified a larger group of children (about 15 per 10,000) who had impairments of social interaction, communication and imagination (which they referred to as the 'triad' of impairments), together with a repetitive stereotyped pattern of activities. Although these children did not fit into the full picture of early childhood autism (or typical autism) as described by Kanner they were identified as being within the broader 'autism spectrum'. Thus, the total prevalence rate for the spectrum in all children with special needs in the Camberwell study was found to be approximately 20 in every 10,000 children (Wing and Gould, 1979). Gillberg et al (1986) in Gothenburg, Sweden, found very similar rates in children with learning disabilities
There has been a number of other epidemiological studies in different countries examining the prevalence of autism (but not the whole spectrum). These results range from 3.3 to 60.0 per 10,000, possibly due to differences in definitions or case-finding methods (Wing and Potter, 2002).
The studies described above identified autistic disorders in children, the great majority of whom had learning disabilities and special educational needs. However, in 1944, Hans Asperger in Vienna had published an account of children with many similarities to Kanner autism but who had abilities, including grammatical language, in the average or superior range. There are continuing arguments concerning the exact relationship between Asperger and Kanner syndromes but it is beyond dispute that they have in common the triad of impairments of social interaction, communication and imagination and a narrow, repetitive pattern of activities (Wing, 1981; 1991).
In 1993, Stephan Ehlers and Christopher Gillberg published the results of a further study carried out in Gothenburg in which they examined children in mainstream schools in order to find the prevalence of Asperger syndrome and other autistic spectrum disorders in children with IQ of 70 or above. From the numbers of children they identified they calculated a rate of 36 per 10,000 for those who definitely had Asperger syndrome and another 35 per 10,000 for those with social impairments. Some of the latter may have fitted Asperger description if more information had been available, but they certainly had disorders within the autistic spectrum. The children who were identified were known by their teachers to be having social and/or educational problems but the nature of their difficulties had not been recognised prior to the study.
For over 30 years, Sula Wolff, in Edinburgh, has studied children of average or high ability who are impaired in their social interaction but who do not have the full picture of the triad of impairments. In her book giving results of her studies (Wolff, 1995), she emphasises that the clinical picture overlaps with Asperger syndrome to a large extent. However, these children represent the most subtle and most able end of the autism spectrum. The majority become independent as adults, many marry and some display exceptional gifts, though retaining the unusual quality of their social interactions.
Why include them in the autism spectrum? As Sula Wolff points out, they often have a difficult time at school and they need recognition, understanding and acceptance from their parents and teachers. The approach that suits them best is the same as that which is recommended for children with Asperger syndrome and high-functioning autism.
In her discussion of prevalence, Sula Wolff quotes Ehlers and Gillberg's study. She considers that their total figure of 71 per 10,000, includes the children she describes.
Autism spectrum disorders
A survey by the Office of National Statistics of the mental health of children and young people in Great Britain found a prevalence rate of 0.9% for autism spectrum disorders or 90 in 10,000 (Green et al, 2005). These were not differentiated into autism, Asperger syndrome or any type of autism spectrum disorder.
Gillian Baird and her colleagues published a report of a prevalence study which surveyed a population of children aged 9-10 years in the South Thames region. All children who either already had a diagnosis of autism spectrum disorder or were known to child health or speech and language services as having social and communication difficulties were selected for screening. Children considered to be at risk of being an undetected case because they had a statement of special educational needs were also selected. Diagnoses were based on ICD-10 criteria. The results showed a prevalence rate of 38.9 in 10,000 for childhood autism, and 77.2 in 10,000 for other autism spectrum disorders, giving an overall figure of 116 in 10,000 for all autism spectrum disorders (Baird et al, 2006).
In this study very few children were identified with Asperger syndrome. The authors acknowledged that some children in mainstream schools who did not have a statement of special educational would have been missed, because of the selection criteria. The authors note that the prevalence estimate found should be regarded as a minimum figure (Baird et al. 2006).
There may be another reason why Asperger syndrome was rarely found in the study. ICD-10 diagnostic criteria for Asperger syndrome are such that a person who would be diagnosed with Asperger syndrome using the criteria used by Gillberg, would probably receive a diagnosis of childhood autism or atypical autism using the ICD-10 criteria.
Prevalence in adults
The Adult Psychiatric Morbidity Survey is the primary data source for monitoring trends in England’s mental health. In 2007 it included for the first time a measure of autism spectrum disorder and found 1% of the population studied had an ASD, (Brugha, T. et al , 2009).
The Department of Health then funded a project to build on the APMS study and look more closely at the numbers of adults with autism that could not have been included in the original study. This included people in residential care settings and those with a more severe learning disability. The study was led by Professor Terry Brugha of the University of Leicester, who also led on autism research for the APMS 2007. Combining its findings with the original APMS, it found that the actual prevalence of autism is approximately 1.1% of the English population, (The NHS Information Centre, Community and Mental Health Team, Brugha, T. et al., 2012).
Recent studies from other countries
The Autism and Developmental Disabilities Monitoring Network in the USA looked at 8 year old children in 14 states in 2008, and found a prevalence rate of autism spectrum disorders within those states overall of 1 in 88, with around five times as many boys as girls affected (Autism and Developmental Disabilities Monitoring Network Surveillance Year 2008 Principal Investigators, 2012).
The National Center for Health Statistics in the USA published findings from telephone surveys of parents of children aged 6-17 undertaken in 2011-12. The report showed a prevalence rate for ASD of 1 in 50, (Blumberg, S .J. et al, 2013).
A study of a 0-17 year olds resident in Stockholm between 2001-2007 found a prevalence rate of 11.5 in 1,000, very similar to the rate found other prevalence studies in Western Europe, ( Idring et al , 2012).
A much higher prevalence rate of 2.64% was found in a study done in South Korea, where the researchers found two thirds of the ASD cases were in the mainstream school population, and had never been diagnosed before., (Kim et al, 2011).
Researchers comparing findings of prevalence studies from different parts of the world over the past few years have come up with a more conservative median estimate of prevalence of 62 in 10,000. They conclude that the both the increase in estimates over time and the variability between countries and regions are likely to be because of broadening diagnostic criteria, diagnostic switching, service availability and awareness of ASD among professionals and the public, (Elsabbagh M. et al, 2012).
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Last updated May 2013