Individual differences in cognitive decline in schizophrenia

The authors' goal was to determine whether cognitively impaired patients with schizophrenia exhibit age-related cognitive declines similar to those of patients with schizophrenia who do not have substantial cognitive impairment. Method: Correlation coefficients were computed between age and the Average impairment Rating, a summary index of cognitive ability, in a group of 77 patients with schizophrenia. These patients were clustered into two groups: one with near-normal cognitive function (N=51) and one with severely impaired cognitive function (N=26). A group of patients with senile dementia (N=21) and another comparison group of nonschizophrenic patients (N=299) were used as reference groups. Results: There were significant correlations between age and the Average Impairment Rating in all groups except the cognitively impaired patients with schizophrenia, in which a zero-order correlation was obtained. Conclusions: Patients with schizophrenia who have substantial cognitive impairment do not have the significant correlation between age and cognitive function found in patients with schizophrenia who have mildly impaired or normal cognitive abilities, suggesting earlier onset of cognitive deficit in the cognitively impaired patients with schizophrenia.