A comparison of reading and demographic-based estimates of premorbid intelligence in schizophrenia

Abstract

Estimating premorbid intelligence in schizophrenia is difficult because the illness affects aspects of premorbid and postmorbid functioning. We evaluated two qualitatively different estimates of premorbid intelligence in a sample of schizophrenia patients and tested whether: (1) the two indices were related and produced similar IQ estimates, and (2) either index was related to a measure of cognitive deterioration. The Barona Index (BI, a demographically-based instrument) and the National Adult Reading Test (NART, a reading test of irregularly-spelled words) were utilized. Subjects (n = 40) were adult neuroleptic-medicated inpatients with a DSM-III-R diagnosis of chronic schizophrenia (n = 35) or schizoaffective disorder (n = 5). Paired t-tests revealed statistically equivalent BI and NART estimates for Full Scale and Verbal IQs, but significantly higher NART Performance IQs (t[35] = -3.34, p < 0.01). Correlational analyses suggested the two indices were associated but shared modest variance. BI correlations revealed expected associations with education and social position. NART IQs were related to education and a measure of cognitive status. Regression analyses supported the association between NART estimates and cognitive deterioration. Results suggest BI may be a better estimate of premorbid intelligence in schizophrenia as it is less influenced by potential consequences of the disease.