How common are Autism Spectrum Disorders (ASD)?

by CDC

ASD Prevalence Questions

What is the prevalence of Autism Spectrum Disorders (ASD)?

Data from several studies that used the current criteria for diagnosing autism and autism spectrum disorders (ASD), such as Asperger's disorder and pervasive developmental disabilities (PDD-NOS), found prevalence rates for ASDs between 2 and 6 per 1,000 individuals. Therefore, it can be summarized that between 1 in 500 (2/1,000) to 1 in 166 children (6/1,000) have an ASD.

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, approximately 24,000 of these children will eventually be diagnosed with an ASD. Assuming the prevalence rate has been constant over the past two decades, we can estimate that up to 500,000 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.

How do the rates of ASDs compare with other childhood disabilities?

A study conducted by the Centers for Disease Control and Prevention, the Metropolitan Atlanta Developmental Disabilities Surveillance Program, found the rate of autism for children ages 3 to 10 years to be 3.4 per 1,000 children which is lower than the rate for mental retardation (9.7 per 1,000 children); but higher then the rates for cerebral palsy (2.8 per 1,000 children), hearing loss (1.1 per 1,000 children) and vision impairment (0.9 per 1,000 children) found in the same study.

Approximately 2% of children under the age of 18 have a serious developmental disability (DD) and these include mental retardation, cerebral palsy, hearing loss and vision impairment. Of these serious DDs, mental retardation (or intellectual disability) is the most common. A genetic disorder often associated with having mental retardation (MR) or an intellectual disability (ID) that many people recognize is Down syndrome. Current information indicate that having Down syndrome occurs in 1 out of 800 births and is slightly less common than the ASDs. Approximately 17% of children have some type of developmental disability, including more mild conditions such as speech and language disorders, learning disabilities, and ADHD, which appear to be more common than the ASDs.

While developmental disabilities may affect a child's speech or language, physical growth, psychological growth, self-care, or learning, children's health may also be affected by diseases that impact adults as well. A common childhood disease, juvenile diabetes, is prevalent in approximately one in every 400 to 500 children and adolescents, which is in a similar range of the ASDs. However, the ASDs are more common than childhood cancer, which has a prevalence rate of 1.5 per 10,000 children (1 in 300 males and 1 in 333 females have a probability of developing cancer by age 20 according to the National Cancer Institute).

How many children with ASDs are being served through public special education programs?

In 2003 approximately 141,022 children were served under the "Autism" classification for special education services. Not all children with an ASD receive special education services under the classification of "Autism", so the education data underestimate the actual prevalence of the ASDs.

How do the rates of ASDs in special education compare with that of other disabilities?

Autism was added as a special education exceptionality in 1991 and is now the 6th most commonly classified disability in the United States. The most common disability classifications in 2003 were: specific learning disabilities (2,866,908 children served), speech or language impairments (1,129,260 children served), mental retardation (582,663 children served), emotional disturbance (484,479 children served), and other health impairments, which often includes children diagnosed with ADHD (452,442 children served). Has the number of children being served under an ASD classification in public special education programs changed? Yes. In 1994 ASDs were the 10th most common disability serving children ages 6-21 in special education. Between 1994 and 2003 the number of children being classified as having an ASD has increased six-fold from 22,664 to 141,022. 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 1990's and the growth of children classified may be in part due to the addition of this as a special education category.

Summary

While, it is clear that more children than ever before are being classified as having an Autism Spectrum Disorder, it is unclear how much of this increase is due to changes in how we identify and classify ASDs in people, or whether this is due to a true increase in prevalence. However, using our current standards, the ASDs are the second most common serious developmental disability after mental retardation/intellectual impairment, but are still less common than other conditions that affect children's development, such as speech and language impairments, learning disabilities, and ADHD. The impact of having a developmental disability is immense for the families affected and for the community services that provide intervention and support for these families. It is important that we treat common DDs, and especially the ASDs, as conditions of urgent public health concern, do all we can to identify children's learning needs, and begin intervention as early as possible to enable all children to reach their full potential.

About the Author

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