Cognitive battery for differential diagnosis of mental retardation vs. psychosis.

Because of their severe cognitive and social deficits, seriously impaired and regressed psychotics are often misdiagnosed as mentally retarded. This diagnostic confusion, which carries dire consequences for treatment, has prevailed due to the lack of objective tests directed at this problem. Procedures are needed to specifically measure and differentiate the hallmarks of the intellectual dysfunction in both conditions (i.e., cognitive abnormality [psychosis] and subnormality [mental retardation]). Such methods also must be adapted to the particular problems and limitations of these populations. We propose here the use of three long established tests and a new developmentally rooted Cognitive Diagnostic Battery, one that assesses conceptual, perceptual-motor, and social maturity. Empirical study supported the validity of this Battery for differential diagnosis between mentally and functionally retarded psychotics matched for IQ, 97% of the developmentally disabled group exhibiting deficits on all three tests of conceptual development vs. 27% in the functionally mentally retarded group.