Using the standardization sample for the WAIS-R, McDermott Glutting, Jones, and Noonan (1989) reported that patterns of intellectual functioning can be categorized into nine prototypal groups. We determined the prevalence of these prototypal patterns in a large sample of neuropsychiatric participants. The vast majority (93.4%) of participants were classifiable into a prototypal group, despite strong differences between the neuropsychiatric and standardization samples with respect to age, gender, occupational status, and education. Neuropsychiatric participants were much more likely to have prototypal patterns associated with low intellectual functioning than were participants in the standardization sample. We conclude that neuropsychiatric morbidity is associated with patterns of low intellectual functioning that are prototypal but that occur at rates much higher than those found in the standardization sample.
