by Elizabeth Aylward,

This article combines a review and meta-analysis of research on IQ in schizophrenia, with emphasis on areas of convergence in the findings, as well as questions that remain to be answered. Taken together, the findings suggest that early-onset and adult-onset schizophrenia are associated with intellectual deficits across the lifespan. Preschizophrenic children, adolescents, and young adults perform below matched controls on a variety of standardized measures of intelligence. Significant IQ deficits are also apparent after the onset of the disorder. Moreover, IQ is positively related to several indices of prognosis, and, among hospi-talized patients, there is negative within-subject covariance between intellectual performance and symptom severity. Although there is fairly consistent evidence that Verbal IQ is higher than Performance IQ among schizophrenic patients, a more specific pattern of subtest performance is not apparent. A central question raised by the results is whether IQ is an independently determined factor that can serve to mitigate the vulnerability of individuals who are constitutionally predisposed to schizophrenia, or whether intellectual deficit is one manifestation of the constitutional predisposition to the disorder. The findings also raise the question of possible sex differences in the developmental determinants of schizophrenia: Meta-analyses revealed that premorbid IQ deficits are more prevalent among males than females. Since the early 1900s when standardized intelligence tests were first being developed, a great deal of speculation and research has been devoted to determining whether relationships exist between IQ and certain forms of psychopathology. Much of the early research in this area sought to discover patterns of subtest performance that could distinguish among diagnostic categories. For example, Wechsler (1958) characterized schizophrenic patients as having high scores on the Information and Vocabulary subtests of, the Wechsler Adult Intelligence Scale, and low scores on the Objec