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Pervasive Development Disorders: Just how Common are They?

written by: Sandi Johnson • edited by: Elizabeth Wistrom • updated: 11/23/2010

How common are Pervasive Development Disorders? It can be difficult to pinned down exact numbers when discussing the prevalence of Pervasive Developmental Disorders. This is due, in large part, to the inaccuracy of testing, diagnosis, and study reports, as well as poor understanding.

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    Average Statistics Concerning PDD

    In trying to determine how common are Pervasive Developmental Disorders (PDD,) a person can quickly become confused by the vast differences in numbers reported. The exact figures are reportedly as common as 1 in 80 children, or as seldom as 1 in 500. Other studies report the number of children diagnosed to be an average of 1 in 110. These studies further site that boys carry a PDD diagnosis as much as four to five times more often than girls. However, these figures are often reported as applied to Autism Spectrum Disorders (ASDs,) rather than all syndromes and disorders categorized under PDD.

    For example, the Autism Society of America reports 1 in 110 births or 1% of the child population in the United States is affected by ASDs. Likewise, the CDC reports that the commonality of ASDs ranges between 1 in 80 and 1 in 240 children between the ages of 3-17. Neither organization reports statistics on Pervasive Developmental Disorders, as a whole. However, many organizations report a rise in the number of children with PDDs in the last 20 years.

    Naturally with improved diagnostic criteria, better screening techniques, and increased awareness, the rate of documented cases has increased. Likewise, since the DSM-III first listed autism as a recognized disorder in 1980, improvements in understanding and inclusion of broader impairments in the diagnostic criteria also increases figures. This does not mean that more children with PDD are born, but that more children with PDD have been identified and officially diagnosed. In the 1960's, based solely on the criteria for classic autism, rates were reportedly 4 in every 10,000 children. Today, the rates for PDD (including all disorders) average a little over 6 in 10,000.

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    PDD, Autism, Asperger's, Isn't It All the Same?

    To the uninitiated, the terms Pervasive Developmental Disorder (PDD) and Autism may seem interchangeable. However, according to the DSM-IV, there is no specific PDD diagnosis. Rather, the PDD label is used as an umbrella term for a variety of neurological disabilities with similar characteristics and symptoms. The confusion and mistakenly interchangeable use of PDD and Autism to mean the same thing can be blamed, in part, to a generic diagnosis known as Pervasive Developmental Delay, Not Otherwise Specified or PDD-NOS.

    When a child’s symptoms and developmental delays do not meet enough predefined criteria for a specific disorder listed under the PDD category, they are often diagnosed with Pervasive Developmental Delay – Not Otherwise Specified. PDD-NOS is a blanket term for children who meet much of the criteria for various autism spectrum disorders or other developmental disabilities, but no one disorder in particular. For example, a child could present with all the classic signs and symptoms of Asperger’s Syndrome with the exception of having no particular subject of obsessive interest. In such cases, since this symptom is so characteristic of Asperger’s, its absence might lead a professional to diagnose a child as PDD-NOS instead.

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    Why Are the Numbers So Varied?

    As an umbrella term, PDD encompasses numerous developmental disabilities beyond just autism spectrum disorders. For example, according to the DSM-IV, Retts Syndrome, and Childhood Disintegrative Disorder (CDD) are also classified under PDD, as well as Autistic Disorder, Asperger's Syndrome, and PDD-NOS. Unfortunately, these disorders are often left out of studies and reported figures concerning how common are Pervasive Developmental Disorders. This may be due to the relatively low occurrence of Retts and CDD compared to autism.

    In a 2003 report published by Auburn University in Canada, Drs. Lee Tidmarsh, MD and Fred R. Volkmar, MD, illustrated the problems with differences in classification of these disorders, which also lends to further confusion. In the report, these doctors highlighted the differences between disorders and diagnostic criteria in the DSM-IV (the American standard for mental health diagnoses) and the ICD-10 (the classification and standards as set by the World Health Organization.) While these two manuals have become closer in terms of standards and inclusions over the years, there are still differences that create difficulties in determining worldwide prevalence. Primarily, the DSM-IV allows for more inclusion of research criteria because the standards are less stringent than the ICD-10.

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    Worldwide Breakdown by Disorder

    • Differences in diagnostic criteria, research information included, manuals used, or the country of origin for different studies aside, the following averages were reported in 2003.
    • Autistic Disorder (Classic Autism) - 10 in 10,000 children
    • Autism Spectrum Disorders (including classic, Asperger's, and PDD-NOS) - 6 in 10,000 children
    • Rett's Syndrome - 1 in 20,000 children
    • Childhood Disintegrative Disorder - 1.7 in 100,000 children
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    References and Resources

    Autism Society of America: http://www.autism-society.org/site/PageServer?pagename=about_whatis_PDD

    Center for Disease Control: http://www.cdc.gov/ncbddd/autism/data.html

    Wrights Law Autism Facts: http://www.wrightslaw.com/info/autism.faqs.nichcy.htm

    Diagnosis and Epidemiology of Autism Spectrum Disorders: http://www.auburn.edu/~lal0011/autism/tidmarsh.pdf