Diagnosis of Mental Retardation in Schizophrenia: Psychometric Distinction Between Intellectual Subnormality and Abnormality

Since many schizophrenics regress cognitively to the point of mental deficiency, the distinction between true (developmental) and functional retardation in the adult poses a recurrent diagnostic problem. Intelligence tests do not resolve the issue, which pivots on the question of whether cognitive processes, though deviant, have fully matured. The present study examined the ability of a series of developmentally rooted cognitive tests and other measures to differentiate between mentally and functionally retarded schizophrenics matched for IQ, sex, and race. Those with true retardation were found to be more primitive in their conceptual strategies, shorter in attention span, and slower in psychomotor pace. As a group, they tended to be younger, hospitalized earlier in life, and less variable on most tests. Optimal performance on each of six measures from the Cognitive Diagnostic Battery provided a statistical basis for ruling out mental retardation in the schizophrenic.