It is difficult to know how many children, teens, and adults have Asperger’s Disorder. Only recognized in the USA since 1994, there has been limited time for researchers to count the true prevalence.
You may have read about dramatic increases in autism and Autism Spectrum Disorder (ASD). Researchers point to two reasons for this increase. Before Asperger’s Disorder gained official recognition in 1994, studies counted only autism, finding 4 cases per 10,000. When Asperger’s Disorder was identified, it was grouped along with autism, and both disorders began to be reported together as the number of individuals with ASD, rather than separate findings for autism and Asperger’s Disorder. The addition of a third diagnosis, Pervasive Developmental Disorder, Not Otherwise Specified (PDD-NOS), has also been added to the numbers. Children with PDD-NOS have symptoms of autism or Asperger’s but not enough to actually be given either diagnosis. They are nonetheless usually counted in the studies and contribute to the rise in the numbers of children reported as having ASD.
The second suspected cause of the dramatic increase in the number of children being diagnosed was the broadening of symptoms that allowed a child to be identified as having autism. Since autism was first included in the Diagnostic and Statistical Manual of Mental Disorders (DSM) in 1980 there have been substantial changes in the way the diagnosis is made, allowing more children to meet criteria for diagnosis than in previous years. Many researchers argue that the changes in the diagnostic criteria are responsible for the increases in autism and ASD, refuting the idea that autism and ASD are actually increasing.
These changes in the way diagnoses are made and counted unfortunately make it impossible to know how many individuals truly have Asperger’s Disorder. We do know that Asperger’s Disorder is more common than autism, with estimates of Asperger’s Disorder occurring in 20–25 per 10,000. Rates of autism for many years were reported as 3–4 per 10,000. However, since the recognition of Asperger’s Disorder, the broadening of autism, and the creation of the term autism spectrum disorders, the numbers have increased dramatically. In 2006 the Center for Disease Control (CDC) reported between 2 and 6 per 1,000 as having ASD. These numbers translate to estimates of 1 per 500 on the low end and 1 per 166 on the high end. This does not mean that 1 in 166 children has autism, as you may have read in many news stories. It is important to understand that the figure of 1 in 166 is the highest estimated number and includes autism, Asperger’s Disorder, and PDD-NOS. Failure to understand these estimates and the changes in diagnosis gives the false impression that autism is on the rise in epidemic proportions.
While it appears that the estimates of autism may be over reported, the incidence of Asperger’s Disorder is probably actually underdiagnosed. Since it is a new disorder, many doctors may not be fully experienced with how to evaluate it. The vague list of symptoms can make it unrecognizable as a disorder, and its overlap with many other disorders may easily cause it to be diagnosed as something else. Until we know more about Asperger’s Disorder, it will likely remain underdiagnosed.