Less Unique Variance Than Meets the Eye: Overlap Among Traditional Neuropsychological Dimensions in Schizophrenia

Abstract

The magnitude of the overlap among dimensions of neuropsychological test performance in schizophrenia has been the subject of perennial controversy. This issue has taken on renewed importance with the recent focus on cognition as a treatment target in schizophrenia. A substantial body of factor analytic literature indicates that dimensions are separable in schizophrenia. However, this literature is generally uninformative as to whether the separable dimensions are independent, weakly correlated, or strongly correlated. Factor analyses have often used methods (ie, principal components analysis with orthogonal rotation) that preclude this determination, and correlations among factor-based domain composites and underlying measures have been reported infrequently in these studies. Current meta-analyses of reported "between-dimension" correlations for individual neuropsychological measures and for cognitive domain composite variables indicate that cognition variables in schizophrenia are correlated, on average, at a "medium" level of r = 0.37 for individual measures from different cognitive dimensions and r = 0.45 for domain composites. Because these are mean bivariate correlations, the multiple correlation of an individual measure with all the other measures in a cognitive battery is likely to be higher. Measure reliabilities of 0.80 or less also imply greater commonality among traditional neuropsychological measures. In short, there are underappreciated constraints on the amount of reliable cognitive performance variance in traditional neuropsychological test batteries that is free to vary independently. The ability of such batteries to reveal cognitive domain-specific treatment effects in schizophrenia may be much more limited than is generally assumed.

Clinical, Functional, and Intertask Correlations of Measures Developed by the Cognitive Neuroscience Test Reliability and Clinical Applications for Schizophrenia Consortium

“…As a point of contrast, a meta-analysis of the bivariate correlations between the types of tasks included in the MATRICS battery yielded a mean correlation of r = .37. 10 Thus, the magnitude of the intercorrelations among tasks observed with the CNTRACS measures are clearly lower than those observed with more standard clinical neuropsychological measures, again consistent with the hypothesis that the CNTRACS measures are assessing more discrete cognitive processes.…”

Effects of Risperidone and Olanzapine Dose Reduction on Cognitive Function in Stable Patients With Schizophrenia: An Open-Label, Randomized, Controlled, Pilot Study

“…This said, the point has been made that a single generalized cognitive score should be used because specified domains do not exist independently. 16 From this perspective, the improvement in the RBANS Total scale score in the reduction group also endorses the benefits of this strategy in enhancing cognition.…”

Cognitive and functional deficits in bipolar disorder and schizophrenia as a function of the presence and history of psychosis

“…Compared to people with bipolar disorder as a group, neurocognitive impairments in schizophrenia are more prevalent and more severe by at least 0.5 effect size units for most domains. 5,8 The profile of neuropsychological impairment in schizophrenia is one of a global deficit, 9 perhaps with superimposed severe deficits in processing speed, verbal learning, and executive dysfunction, 10,11 whereas clinically stable individuals with bipolar disorder tend to have more severe and persistent impairments in processing speed and verbal memory, with spared performance on tests that index perceptual and visuomotor skills. 5 Finally, the stability of neurocognitive impairment is quite remarkable in schizophrenia, whereas the limited data available suggest that for many individuals with bipolar disorder cognitive impairments may be more closely related to symptom state, with impairments in verbal learning exacerbated during manic/mixed states, 12 impairments in verbal fluency exacerbated during depressed states, 12 and improvement of some abilities during periods of euthymia.…”