A summary of the CDC autism prevalence report

by Matt Carey

There has been a great deal of media coverage recently about the new autism prevalence estimate released by the CDC. The CDC provides a good summary page on prevalence data as well as the full report. If those who may see the report as a bit long, here is a bit of a summary of the findings.

The United States Centers for Disease Control (CDC) releases autism prevalence estimates as part of their MMWR (Morbidity and Mortality Weekly Report). They also maintain a page of information on autism. Today the CDC released the latest MMWR on autism: Prevalence of Autism Spectrum Disorders — Autism and Developmental Disabilities Monitoring Network, 14 Sites, United States, 2008. The one number from it that will be quoted most often is “1 in 88”, the new prevalence estimate.

The researchers working for the CDC use existing records: school, medical or both. So, in one area they may use school records. In another they may use school and medical records. What they don’t do is actually screen individual children and give them tests like the ADOS. This means that if a kid is not flagged somewhere in the records, they won’t find him/her. On the other hand, they don’t just count which kids already have autism diagnoses. They review the records and evaluate them to determine which kids are autistic or not. They cross check, meaning that for some fraction of the kids they use more than one person to check the records and they see how well the various researchers agree.

The CDC works with groups in a subset of states in the U.S.. For this report they used Alabama, Arizona, Arkansas, Colorado, Florida, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah, West Virginia, and Wisconsin, most of which were used in previous reports.

Overall, the prevalence was 1 in 88 (11.3 per 1,000). This continues the upward trend in prevalence estimates from the CDC. This figure (here for bigger) is from the CDC:

This varied a great deal state-to-state. Alabama had the lowest estimated prevalence at 4.1 per 1,000. Utah the highest at 21.2 per 1,000. Or, there is about a five fold variation in autism prevalence estimates, state-to-state.

Prevalence estimates also varied by race/ethnicity. The report states “the estimated prevalence among non-Hispanic white children (12.0 per 1,000) was significantly greater than that among non-Hispanic black children (10.2 per 1,000) and Hispanic children (7.9 per 1,000). ” The estimate for Hispanic in Alabama was 1.4 per 1,000 and for whites in Utah as 40 per 1,000. More than a 20 fold difference.

This figure (click to enlarge)was interesting in showing two things. First in showing the state-to-state variability in prevalence estimates. The second interesting point to me is the difference between sites with just medical records and those with medical and education records. The sites with health-only records have lower prevalence estimates. i.e. more kids are picked up by their school records.

As with previous CDC reports, a large fraction of the children identified were not classified as autistic previously. This figure (click to enlarge) shows state-by-state and year-by-year what percent were previously unidentified. The figure also shows how many were previously unidentified but where a suspicion of autism was noted. In 2002, as many as 40% in some states were not classified as autistic before their records were reviewed. In general, over time the fraction previously unidentified has gone down. This would be consistent with schools and medical personnel getting better over time with identification of autism.

Many children identified had IQ test scores (or examiner statements) showing “normal” or borderline-normal values. This figure (click to enlarge) shows the percentages in many states with IQ>85, IQ=71–85 and IQ<70 (for children where the IQ data were available).

In Utah, for an extreme example, over 70% of those identified as autistic have IQ scores above 85. The CDC report reads:

When data from these seven sites were combined, 38% of children with ASDs were classified in the range of intellectual disability (i.e., IQ >70 or an examiner’s statement of intellectual disability), 24% in the borderline range (IQ 71–85), and 38% had IQ scores >85 or an examiner’s statement of average or above-average intellectual ability.

I.e. most children were borderline or above. Of course, the other way to read this is most children were borderline or below. Intellectual Disability is roughly defined as IQ below 70, so most children (about 62%) identified as autistic in this report were not intellectually disabled. States with higher prevalence estimates had higher percentages of non-intellectually disabled children.

The prevalence estimates are going up with time.

While ASD prevalence estimates in the overall population increased 23% for the 2-year period 2006–2008, and 78% during the 6-year period 2002–2008, the largest increases over time were noted among Hispanic children and non-Hispanic black children and among children without co-occurring intellectual disability. Better identification in these specific groups explains only part of the overall increase, however, as estimated ASD prevalence increased in all groups when data were stratified by sex, race/ethnicity, and intellectual ability.

The CDC report does have some limitations, and they note two primary limitations:

First, increases in awareness and access to services have improved the ability of the ADDM Network to identify children with ASD over time, and this likely contributes to the increase in estimated prevalence. The proportion of the increase that is attributable to such changes in case ascertainment or attributable to a true increase in prevalence of ASD symptoms cannot be determined. Ongoing monitoring is an important tool to learn why more children are being identified with ASDs and can provide important clues in the search for risk factors.

This study can’t say if there is an increase in the number of autistic children, or if there is, what would be the cause.


Second, the surveillance areas were not selected to be representative of the United States as a whole, nor were they selected to be representative of the states in which they are located. Limitations regarding population size, surveillance areas, and the consistency of these attributes were considered when analysts evaluated comparisons across multiple time points.

So, these numbers may not represent the United States as a whole.

It is valid to say that while these factors limit the ability of the CDC to define a true autism rate for the United States, the factors that go into these limitations are valid research concerns in themselves. It is very much worthwhile and valuable to ask why there are such variations state-to-state, for example. Answering this could lead to better identification and service provision overall. Likewise, understanding the effects of rising awareness could feed back into more efficient awareness campaigns to, again, help in identifying more autistic children and providing support and services to them.

The CDC concludes:

ASDs continue to be an important public health concern. The findings provided in this report confirm that prevalence estimates of ASD continue to increase in the majority of ADDM Network communities, and ongoing public health surveillance is needed to quantify and understand these changes over time. Further work is needed to evaluate multiple factors affecting ASD prevalence over time. ADDM Network investigators continue to explore these factors in multiple ways, with a focus on understanding disparities in the identification of ASDs among certain subgroups and evaluating temporal changes in the prevalence of ASDs. CDC also is engaged with other federal, state, and private partners in a coordinated response to identify risk factors for ASDs and meet the needs of persons with ASDs and their families. Additional information is available at http://www.cdc.gov/autism.

We need these data. Limitations and all. We need to know what the autism prevalence is, what the makeup is of the autistic population, and where we can do better identifying autisics. Most countries have no autism prevalence information. Other countries have few or even just one study. In my opinion we are fortunate to have the CDC and other researchers focusing on these questions here in the United States.

1 in 88 Diagnosed with ASD, CDC Reports (1 in 54 Boys)

From Autism Science Foundation

(March 29, 2012—New York)  The Centers for Disease Control in Atlanta today reported that 1 in 88 children were diagnosed with an autism spectrum disorder (ASD) in 2008.  That’s a 23% increase from 2006 when the prevalence rate was 1 in 110.  Autism spectrum disorders are almost five times more common among boys than girls – with 1 in 54 boys identified.

“One thing the data tells us with certainty – there are many children and families who need help,” CDC Director Thomas Frieden, M.D., M.P.H said in a press release. “We must continue to track autism spectrum disorders because this is the information communities need to guide improvements in services to help children.”  On a noontime call with media and advocates, Dr. Frieden added “Doctors are getting better at diagnosing autism. It’s possible that the increase is entirely the result of better detection.”

The identified prevalence of ASDs in U.S. children aged 8 years was estimated through a retrospective review of records in multiple sites participating in the CDC’s Autism and Developmental Disabilities Monitoring (ADDM) Network. Data were collected from existing records in 14 ADDM Network sites (Alabama, Arizona, Arkansas, Colorado, Florida, Georgia, Maryland, Missouri, New Jersey, North Carolina, Pennsylvania, South Carolina, Utah and Wisconsin) for 2008.  Children aged 8 years met the case definition for an ASD if their records documented behaviors consistent with the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, text revision (DSM-IV-TR) criteria for autistic disorder, pervasive developmental disorder–not otherwise specified (PDD NOS), or Asperger disorder. Presence of an identified ASD was determined through a review of data abstracted from developmental evaluation records by trained clinician reviewers.

“These are not just numbers, these are real people with real needs” said Alison Singer, president of the Autism Science Foundation.  “These are families that are exploding.  We have to focus on building the infrastructure to provide education and services to all of these people and their families. And we have to focus on what is fueling the increase in prevalence, and that means investing in research.  We have learned so much about autism’s genetic underpinnings in the last few years. We have to understand more about what’s going wrong in the brain that causes autism so that we can develop appropriate medical treatments.”

“We need to accelerate research into causes” said Dr. Coleen Boyle, Director of the CDC’s Center for Birth Defects and Developmental Disabilities.  “Tracking helps identify potential risk factors. Because of tracking we now know more about how advanced parental age and premature birth confer increased risk for autism.”

Autism spectrum disorders (ASDs) are a group of developmental disabilities characterized by atypical development in socialization, communication, and behavior. ASDs typically are apparent before age 3 years and sometimes can be diagnosed as early as 14 months, with associated impairments affecting multiple areas of a person’s life. Because no biologic marker exists for ASDs, identification is made by professionals who evaluate a child’s developmental progress to identify the presence of developmental disorders.

Learn more at www.autismsciencefoundation.org.  646-723-3976

Read the full report from CDC  http://www.cdc.gov/mmwr/preview/mmwrhtml/ss6103a1.htm?s_cid=ss6103a1_e

CDC has also issued a Community Report  that gives detail by site and has a useful FAQ section.




ASF Strongly Supports Combating Autism Reauthorization Act of 2011

The Autism Science Foundation (ASF) strongly supports the Combating Autism Reauthorization Act of 2011 (CARA) introduced today by Senator Robert Menendez (D-NJ) and Senator Mike Enzi (R-WY) in the United States Senate and by Rep. Chris Smith (R-NJ) and Rep. Mike Doyle (D-PA) in the United States House of Representatives. 

The new bill reauthorizes the Combating Autism Act of 2006 (CAA), which has played a critical role in advancing autism research and treatment.  The original CAA, set to sunset on September 30, 2011, expanded federal investment for autism research through NIH, increased services, diagnosis and treatment through HRSA, and enhanced surveillance and awareness efforts by the CDC.  The CAA authorized nearly $1 billion in federal research spending over five years—increasing autism research spending by almost 50 percent.  This research has led to improved understanding of the causes of autism and has helped us begin to develop new interventions.  Additionally, the research funded through CAA has increased the ability of professionals to more properly screen, diagnose, and treat individuals with autism. The Combating Autism Reauthorization Act of 2011 ensures that the programs established under the original law continue for an additional three years, including CDC surveillance programs, HRSA intervention and training programs, and the Interagency Autism Coordinating Committee (IACC).

The Autism Science Foundation strongly supports this new legislation and urges all members of Congress to act swiftly to pass it into law.  We thank Senator Menendez, Senator Enzi, Congressman Doyle and Congressman Smith for their continued focus on the needs of individuals with autism and their families. We look forward to continuing to work with them and the broader autism community to ensure passage of this important legislation.  At an IACC meeting earlier this year, the Obama administration pledged to support CARA and to sign the bill into law upon passage.

The Autism Science Foundation is 501(c)3 public charity. Its mission is to support autism research by providing funding and other assistance to scientists and organizations conducting, facilitating, publicizing and disseminating autism research. The organization also provides information about autism to the general public and serves to increase awareness of autism spectrum disorders and the needs of individuals and families affected by autism.

Science and Sandwiches Event Focuses on Need for Better Understanding of Autism Prevalence

Dr. Grinker, Former First Lady Rosalynn Carter and ASF President Alison Singer at "Science and Sandwiches"
Dr. Grinker, Former First Lady Rosalynn Carter and ASF President Alison Singer at "Science and Sandwiches"

The Autism Science Foundation’s “Science and Sandwiches” program this week featured a presentation  by Dr. Richard Grinker, Professor of Anthropology at George Washington University and author of critically acclaimed and extremely popular book “Unstrange Minds: Mapping the World of Autism”.  Dr. Grinker spoke about the science of autism as a cultural system. He emphasized the importance of culture in understanding how societies view illnesses, and discussed how in a variety of different historical contexts, radical shifts in how illnesses are identified, treated, and counted resulted not from new scientific discoveries but from cultural changes. Grinker then noted that a number of factors produced the global rise in autism awareness, with some being more salient than others depending upon cultural context. For example, autism awareness has increased significantly in South Korea as the result of a new documentary film, highlighting both the strengths and deficits of people with autism and their families, while in the United States, awareness was a result of deinstitutionalization, diagnostic substitution, and changes in disability rights, among others, all acting in concert.

Despite the increase in awareness, Grinker noted that there is little scientific knowledge about ASD outside of North America and Western Europe.  Indeed, there are insufficient data to estimate the prevalence of autism in the Caribbean, Central and South America, Eastern Europe, the Middle East, South and Southeast Asia, and the entire continent of Africa. Although, he said, most researchers expect that the onset and core symptoms of ASD are consistent across cultures, this remains an assumption. He stated that ASD experts to date know little about how genetic heterogeneity and cultural differences interact to influence the kind and range of impairments that are associated with ASD, its prevalence, course, or familial patterns. He concluded by praising advocates – including his own autistic daughter – for showing that autism can be reconfigured as possibility rather than limitation.

Additional “Science and Sandwiches” presentations are currently being planned for Philadelphia, South Florida and New York City. If you’re interested in hosting an event, write to contactus@autismsciencefoundation.org

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