An increasing body of evidence on the structure of psychopathology indicates the presence of a general factor of psychopathology (GF), also referred to as a P-factor, that explains a significant amount of the common variance in the expression of multiple psychopathological symptoms and disorders. The presence of a GF has substantial implications for understanding psychopathology because it suggests that a comprehensive understanding of mental illness requires an untangling of nonspecific risk factors from more narrow, dimension- specific risk factors or features. Caspi et al., (2014) suggest that schizophrenia symptoms are so highly correlated with the GF, that they are mostly an expression of the GF. However, methodological limitations, such as the use of community and youth samples, limit conclusions from the existing literature. We propose to test the hypothesis that schizophrenia spectrum (SS) symptoms load heavily on both a GF AND a separate higher-order psychosis factor using a sample of 1000 adult psychiatric and medical treatment seeking subjects that includes a substantial group of patients with SS disorders as well as patients with significant externalizing and internalizing symptoms. The potential utility of this hierarchical dimensional approach is that it allows quantification of the extent to which each individual possesses a high GF score (reflected in the overall breadth of symptoms), or symptoms that are more narrowly constrained to a specific 2nd order factor (such as externalizing, internalizing, and psychosis factors) or even more narrow, first-order symptom dimensions. Using this quantitative approach, we will test the extent to which neuropsychological and structural and functional MRI measures that have previously been observed in patients with schizophrenia are more strongly related to the GF versus a psychosis factor. This will allow us to test the hypothesis that some neural correlates, such as the volume of the anterior cingulate area, are nonspecific correlates of the GF, while others, such as temporal cortical sensory processing abnormalities, are specific to the psychosis, and remain even after controlling for the GF. In order to test the prognostic significance of the GF, we will additionally test whether scores on the GF are predictive of course of illness in 50 SS patients experiencing first-episode psychosis. Taken together, the study will provide the most comprehensive test to date of the relevance of GF model to understanding the expression and neural correlates of severe psychopathology,
In order to understand psychotic disorders, it is essential to distinguish which features and risk factors are specific to the disorders and which features are common to multiple types of psychopathology. We propose an approach that allows quantification of these common and specific features of psychosis. This has significant implications for clinical assessment, prognosis and research into the etiology of psychosis.
