Structure of positive psychotic symptoms in individuals at clinical high risk for psychosis

Aim: Positive symptoms are a critical dimension of psychopathology in psychotic disorders and are used as a criterion for diagnosis across the psychosis continuum. Although initially considered as one dimension, there is evidence for multidimensionality within positive symptoms. The positive symptom structure has not been examined in individuals at clinical high risk (CHR) for psychosis. Knowledge of the dimensional structure of positive symptoms within CHR may contribute to our understanding of the aetiology and trajectory of this key facet of psychosis. Method: Exploratory factor analysis (EFA) was conducted on the Prodromal Questionnaire-Brief for 183 individuals meeting CHR criteria. Internal consistency was examined to determine the hierarchical structure of the data and alternative models were compared. Results: EFA revealed a three factor model, grouping in to: perceptual abnormalities, grandiose/unusual delusions and persecutory/thought delusions, with a general factor accounting for 56% of the variance. Confirmatory factor analysis showed that a hierarchical model was the best fit. One item referring to nihilistic thoughts did not load on any factor. Conclusion: There is a clear three-dimensional model, distinguishing perceptual abnormalities, and two subgroups of delusions in CHR individuals. The factors are similar to those found in psychotic disorders. The identification and comparison of symptomatic models is useful given the prominent role positive symptoms play in diagnosis, and is crucial to our understanding of the clinical progression of psychosis. This work may provide a useful tool for future studies examining correlations with varying symptom factors and disease progression in CHR.