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Prevalence of ASDs
It is clear that more children than ever before are being
classified as having autism spectrum disorders (ASDs). But, it is
unclear how much of this increase is due to changes in how we
identify and classify ASDs in people, and how much is due to a true
increase in prevalence. By current standards, ASDs are the second
most common serious developmental disability after mental
retardation/intellectual impairment, but they are still less common
than other conditions that affect children’s development, such as
speech and language impairments, learning disabilities, and
attention deficit/hyperactivity disorder (ADHD). The impact of
having a developmental disability is great for the families affected
and for the community services that provide intervention and support
for these families. It is important that we treat common
developmental disabilities, and especially ASDs, as conditions of
urgent public health concern, do all we can to identify children’s
learning needs, and start intervention as early as possible to give
all children the chance to reach their full potential.
What is the
difference between “incidence” and “prevalence”?
Incidence is the
number of new cases of disease in a defined group of people over a
specific time. Prevalence is the number of existing disease cases in
a defined group of people during a specific time period.
Public health professionals use prevalence measures to track a
condition over time and to plan responses at local, regional, and
national levels. Incidence is very difficult to
establish because the exact time a person develops an ASD is not
known.
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What is the
prevalence of autism?
CDC’s Autism and Developmental Disabilities Monitoring (ADDM) Network released data in 2007 that found about 1
in 150 8-year-old children in multiple areas of the United States
had an ASD.
Since the ADDM sites do not represent a nationally representative
sample, the prevalence estimates should not be generalized to every
community in the United States. Although accurate for the areas we
studied, rates may be higher or lower in other areas. However, these
prevalence estimates can help communities project how many children
may have autism for planning and identification purposes. They can
also be used to provide for more appropriate interventions for
children with ASDs.
What do the ADDM network results tell us
about the prevalence of ASD in the United States?
Results from CDC’s ADDM network
showed the average ASD prevalence among states participating in the
project was 6.7 per 1,000 children in 2000 (6 sites) and 6.6 per
1,000 in 2002 (14 sites), or approximately 1in 150 children. Most
sites identified between 5.2—7.6 per 1,000 8-year-old children with
ASD in 2000 and 2002. There was some variation with ASD prevalence
significantly lower in 1 site (3.3 in AL) and higher in 1 site (10.6
in NJ). Prevalence was stable from 2000 to 2002 in 4 of the 6
sites that participated in both surveillance years, but increased
slightly in GA and significantly in WV, indicating the need for
ongoing monitoring of prevalence over time. These data provide
important information on the prevalence of ASD in areas of the
United States and will be used to examine trends in the occurrence
of these disabilities over time.
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What did we know about the prevalence of Autism Spectrum
Disorders (ASDs) before ADDM?
For decades, autism was believed to occur in 4 to 5 per 10,000
children. In 2004, CDC partnered with the American Academy of Pediatrics (AAP)
to issue an Autism A.L.A.R.M.[1]
At that time, Data from
several studies that used the current criteria for diagnosing ASDs (DSM-IV
and ICD-10) found prevalence rates
for ASDs between 2 and 6 per 1,000 children. Therefore, it was
summarized that up to 1 in 166 children (6/1,000) have an ASD.
While the 1in166 indicated the average upper estimate, there have
been studies that have found as many as 12 in 1,000 children with an ASD in Europe and Scandinavia. Studies conducted specifically in
the United States have found rates between 2 to 7 per 1,000
children in the past decade.
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How
many children in the United States have an ASD?
There is not a full population count of all individuals with an
ASD in the United States. However, using the prevalence data stated
above, we can estimate that if 4 million children are born in the
United States every year and assuming the prevalence rate has been
constant over the past two decades, we can estimate that up to
560,000 individuals between the ages of 0 to 21 have an ASD.
However, many of these individuals may not be classified as having
an ASD until school-age or later. Since behaviors related to the
ASDs are usually present before the age of 3 years, it is important
to make sure the individuals are being identified and are receiving
appropriate intervention services as early as possible.
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How many children with ASDs are being served through public
special education programs?
In 2006, 224,594 children ages 6-21 and 35,111 children ages 3-5
were served under the “autism” classification for special education
services[2]. Not all children with an ASD receive special education
services under the classification of “autism,” so the education data underestimate the actual prevalence of ASDs.
For more information about children served through public education
programs, go to the
IDEA data
website.
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Has the number of children being served under an ASD
classification in public special education programs changed?
Yes. Between 1994 and 2006, the number of 6 to 17-year-old
children classified as having an ASD in public special education
programs increased from 22,664 to 211,610.[2]
While it is clear that more children are getting special
education services for autism than ever before, it is important to
remember that this classification was only added in the early 1990s.
Growth in the number of children classified may be caused in part by
the addition of autism as a special education category.
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Why do we need to
know the prevalence of ASDs?
Families, public agencies, and some private agencies
bear the responsibility of paying for costly services involved in
educating and treating symptoms associated with ASDs. Accurate
reporting of ASD prevalence can help people plan for the resources
needed such as therapies, trained teachers, diagnosticians, health
care providers, and related service professionals. A recent study (Ganz
2006) indicated that the economic costs associated with
autism are approximately $35 billion dollars per year; not to
mention the untold challenges that families face in understanding
their family member with ASD. Planning for housing and job training
also require accurate numbers over time. Accurate reporting of ASDs
over time and from different communities can also help to answer the
question, is their variability in ASDs in different areas of the
country or in different groups of people? Precise reporting of ASDs
leads to better planning by service providers, and helps to provide
justification for limited research dollars from public and private
sectors. Precise reporting of ASDs can also lead to greater
awareness, encourage commitment by service providers and
researchers, and help lead the way to more effective intervention
and prevention.
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What is CDC doing to
understand the prevalence of ASDs in the United States?
CDC has set up the only
collaborative network to determine the prevalence of the ASDs in the
United States. The Autism and Developmental Disabilities Monitoring
(ADDM) Network is made up of scientists working in 10 sites across the nation, in addition to CDC.
Metropolitan
Atlanta Developmental Disabilities Surveillance Program
(MADDSP).
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How do the rates of ASDs in special education compare with those
of other special education categories?
In 2006, according to
IDEA
administrative counts,
6,580.679 children children ages 6–21 received
services through 13
categories
in public special education programs. Specific learning disability
was the most frequent education category identified, and speech and
language impairment was second. Together, these two categories made
up nearly 65% of all special education placements. The mental
retardation classification made up about 9% (523,240). Autism made
up about 4% (224,594).[2]
CDC’s Metropolitan Atlanta Developmental Disabilities Surveillance
Program (MADDSP ) found the autism rate among
8-year-old children in 1996 to be 4.2 per 1,000.[3]
That’s lower than the rate for mental retardation (15.5 per 1,000)
but higher than the rate for cerebral palsy (3.6 per 1,000), hearing
loss (1.4 per 1,000), and vision impairment (1.4 per 1,000) found
among children of the same age.[4]
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How do ASD
rates compare with rates of other disabilities and diseases
diagnosed in children?
Down syndrome, the most
commonly identified cause of mental retardation, occurs in about 1
in 800 births.[5]
Juvenile diabetes, a common childhood disorder, occurs in about 1 in
400 to 500 children and adolescents,[6]
which is similar to the lower range of the ASD rates of 1 in 500.
However, ASDs are more common than childhood cancer, which has a
prevalence rate of 1.5 per 10,000 children, according to the
National Cancer Institute.[7]
For more information on autism prevalence, see
“Determining
How Many Children Have ASDs.”
Links
Autism Fact Sheet
(National Institute of Neurological Disorders and Stroke)
Autism Spectrum Disorders Fact Sheet
(National Center on Birth Defects and Developmental Disabilities)
Disclaimer: We have provided a link to
these sites because they have information that may be of interest to you. CDC does not necessarily endorse the views or information presented on
these sites. Furthermore, CDC does not endorse any commercial products or information that may be presented or advertised on these sites.
References
[1] American
Academy of Pediatrics, The National Center of Medical Home
Initiatives for Children with Special Needs:
http://www.medicalhomeinfo.org/health/Autism%20downloads/AutismAlarm.pdf
[2]
Individuals with Disabilities Education Act (IDEA) Data.
Number of children served under IDEA Part B by disability and age
group, 2006. [cited Jan 2008]. Available at:
https://www.ideadata.org/arc_toc8.asp#partbCC.
[3]Metropolitan
Atlanta Developmental Disabilities Surveillance Program. [cited
2006 Nov]. Available at:
http://www.cdc.gov/ncbddd/dd/ddsurv.htm#prev.
[4] Karapurkar Bhasin T, Brocksen S, Nonkin Avchen
R, Van Naarden Brau, K. Prevalence of four developmental
disabilities among children aged 8 years - The Metropolitan
Atlanta Developmental Disabilities Surveillance Program, 1996
and 2000. MMWR Morbidity and Mortality Weekly Reports 1996;55
(SS01):1-9.
[5] National Center on Birth Defects and
Developmental Disabilities. Key Findings from Recent Birth
Defects and Pediatric Genetics Branch Projects. [cited 2006
Nov]. Available at:
http://www.cdc.gov/ncbddd/bd/ds.htm.
[6] National Center for Chronic Disease Prevention
and Health Promotion. National Diabetes Fact Sheet. [cited 2006
Nov]. Available at:
http://www.cdc.gov/diabetes/pubs/estimates.htm#prev2.
[7] Gloeker Ries LA, Percy CL, Bunin GR. Cancer
Incidence and Survival among Children and Adolescents: United
States SEER Program 1975–1995. National Cancer Institute. [cited
2005 Jan 21]. Available at:
http://seer.cancer.gov/publications/childhood.
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Date:
January 30, 2008
Content source: National Center on Birth Defects and Developmental
Disabilities
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