Once a pervasive developmental disorder is diagnosed, the diagnosis must be narrowed to one of the five types, which is achieved by using pre-established DSM criteria that outline the key differences among the types.
The DSM IV makes a clear distinction between Aspergers and other pervasive developmental disorders in that the condition does not include the profound delays in communication and cognitive development.
The number comes from the APA's Diagnostic and Statistical Manual of Mental Disorders (DSM), a periodically revised guidebook containing all of the mental health issues recognized by the APA.
Pervasive developmental disorders are diagnosed using the Diagnostic and Statistical Manual of Mental Disorders (DSM), which provides criteria for physicians to diagnose the specific type.
The American Psychiatric Association's Diagnostic and Statistical Manual of Mental Health Disorder, Fourth Edition, Revised Text (DSM IV-TR), refers to atypical autism as PDD-NOS.