Measurement Issues:The Psychometrics of Psychosis- Assessing and rating perceptual and ideational disturbance in adolescents

Background: The early recognition and management of psychosis spectrum disorders is associated with superior outcomes in affected individuals. However, this can be challenging for numerous reasons. This article provides perspectives on the effective evaluation and rating of potentially psychotic phenomena young people. We compare and contrast two widely used instruments that can support this process. Findings: The Comprehensive Assessment for At-Risk Mental States (CAARMS) is used to explore potentially psychotic experiences in young people perceived to be at risk of an emerging or imminent psychosis. There is evidence to support its reliability and, to some extent, the predictive validity of the resultant scores. However, relatively low short–medium transition rates to psychosis in ‘positive’ cases suggest that its use as a screening instrument should be restricted to groups who show some indication of impending risk (e.g. help-seeking, distress, declining functioning, perceptual disturbance, etc.). In contrast, the Positive and Negative Syndrome Scale (PANSS) is calibrated to rate symptoms in those with an established psychosis, especially those with a diagnosis related to the schizophrenia spectrum. Consequently, the PANSS is useful for evaluating the clinical course and outcomes of psychotic illness. Conclusions: Although neither instrument is designed specifically for use in those under 18, with care they can be used to effectively support the management of adolescents reporting perceptual and ideational disturbance. However, it is important that any instrument ratings are placed meaningfully in the context of the overall clinical picture and all available information.