It’s important to understand how the diagnosis of Autism is made.  For a child to be diagnosed with Autism, they must have difficulty socially interacting with others; they must have impairments in communication; and they must also show restricted interests.  Autism is considered a neurological disorder and to date, has no biological marker.  There are currently no blood or chromosomal tests that identify Autism.  What we find is that Autism looks very different from one child to the next because, "the expression of these symptom areas can vary considerably" (Koegel & LaZebnik, 2004).  To make things even more difficult, most children have these behaviors to some extent.  So the question is not "if" a child has one or more of these symptoms, it's the "extent they have one or more of these symptoms."  In recent years, advocates and professionals in the field have begun referring to this range of differences as" Autism Spectrum Disorder" or ASD. 

To complicate things even further, other PDD diagnosis are being included in the Autism Spectrum such as Asperger's and PDD-NOS.  With Asperger's, a child demonstrates deficits in social interaction and has restricted interests, but no communication impairments.  PDD-NOS is commonly referred to as A-typical autism in which a child demonstrates only 2 of the 3 qualifying deficits.  Typically, children with a diagnosis of PDD-NOS demonstrate difficulties with social interaction and have deficits in either communication or restricted interests.

Over the last decade, Autism has taken its hold on the “consciousness” of society.  There is no argument as to whether the incidence of Autism has risen over this time period.  The factors associated with the rising prevalence, like so many other factors associated with this diagnosis, have proven to be elusive and controversial.   The DSM-4 states that Autism occurs in 5-15 children per 10,000 born.  Yet Autism Speaks, the nation's largest autism advocacy group sponsor's commercials claiming "autism strikes 1 out of 150 children" (Autism Speaks, 2008).  Why is there such a large discrepancy?  The discrepancy has much to do with what diagnoses are included in these statistics.   For example, when Autism Speaks states that 1 out of 150 children are diagnosed with “autism”, they are including the prevalence data from all five (5) of the Pervasive Developmental Disorders (Autism, Asperger’s, Rett’s Disorder, Childhood Disintegrative Disorder, and PDD-Not Otherwise Specified) in their statistics. 

It’s widely accepted in professional and advocacy communities that the incidence of autism has increased in frequency over the past several years and continues to do so.  The reasons are varied, controversial and a source of continuing inquiry and research.   Some researchers have suggested “diagnostic substitution” as one reason for the increased prevalence.   Shattuck (2006) studied changes in U.S. special education classification categories for 6 through 11 year olds from 1984 to 2003 and found a 3.1 per 1000 increase in the autism classification while at the same time a 2.8 decrease in the mental retardation classification. 

Some researchers have suggested that although diagnostic substitution does have some part in the increased prevalence rate, it does not account for all of the increase.  Coo, Ouellette-Kuntz, Lloyd, and Kasmara (2008) examined trends in assignment of special education codes to British Columbia school children who had an autism code in at least 1 year between 1996 and 2004.  They found that diagnostic substitution accounted for at least one-third of the increase in autism over the study period.  Croen, Grether, Hoogstrate, and Selvin (2002) suggested that the increase in prevalence is in some part a reflection of the “true” rate of autism that has always existed in the population.  

Others have suggested reasons such as an increase in the awareness of autism, better diagnostic technology, and changes in case definitions (Fombonne, 2003; Web, et al., 1997; Wing, & Potter, 2002).  Until more definitive studies emerge, it seems parsimonious to assume that all of these factors contribute in some fashion to the observed rise in autism prevalence.

At this time, the best conservative estimate of the prevalence rate of autism in our population is 13 per 10,000 (Fombonne, 2007).

REFERENCES

Autism Speaks. (n.d.). Retrieved February 12, 2009 from http://www.autismspeaks.org .

Coo, H., Ouellette-Kuntz, H., Lloyd, J.E. V., Kasmara, L., Holden, J.J. A., Lewis, M.E.S. (2008). 
    Trends in autism prevalence: Diagnostic substitution revisited. Journal of Autism &     
    Developmental Disorders, 38,(6), 1036-1046.

Croen, L.A., Grether, J.K., Hoogstrate, J., Selvin, S. (2002). The Changing Prevalence of 
    Autism in California. Journal of Autism and Developmental Disorders, 32, (3).

Fenske, E. C., Zalenski, S., Krantz, P.J., & McClannahan, L.E. (1985). Age at intervention and 
    treatment outcome for autistic children in a comprehensive intervention program. Analysis 
    and Intervention in Developmental Disabilities, 5, 49-58.

Fombonne, E. (2003). Epidemiological surveys of autism and other pervasive developmental 
    disorders an update. Journal of Autism and Developmental Disorders, 33, 365–382.

Fombonne, E. (2007). Epidemiology of pervasive developmental disorders. In J.M. Perez, P.M. 
    Gonzalez, M.L. Comi, and C. Nieto (eds) New Developments in Autism: The Future Is     
    Today. London: Jessica Kingsley Publications.

Koegel, L.K., LaZebnik, C. (2004). Overcoming autism: Finding the answers, strategies, and 
    hope that can transform a child’s life. London: Penguin Books

Shattuck, P. (2006). The contribution of diagnostic substitution to the growing administrative 
    prevalence of autism in U.S. special education. Pediatrics, 117, (4), 1028-1037.

Webb, E. V., Lobo, S., Hervas, A., Scourfield, J., & Fraser, W. I. (1997). The changing  
    prevalence of autistic disorder in a Welsh health district. Developmental Medicine and Child 
    Neurology, 39, 150–152.

Wing, L., & Potter, D. (2002). The epidemiology of autistic spectrum disorders: Is the 
    prevalence rising? Mental Retardation and Developmental Disability Research Review, 8, 
    151–161.