The Inventory of Psychotic-Like Anomalous Self-Experiences (IPASE): Development and Validation

Anomalous self-experiences (ASEs) are among the first symptoms to appear in the prodrome, predict the development of psychosis over and above clinical symptoms, and are common in people with schizophrenia. Although there are well-validated phenomenological interviews for assessing ASEs, there are no self-report measures. The current research describes 4 studies designed to develop and validate a new scale to assess ASEs: the Inventory of Psychotic-Like Anomalous Self-Experiences (IPASE). In Study 1, an overinclusive item pool was generated based on phenomenological descriptions of ASEs, and items were kept or discarded based on factor loadings in an exploratory factor analysis. Five factors were extracted including disturbances in Cognition, Consciousness, Self-Awareness and Presence, Somatization, and Transitivism/Demarcation. The 5-factor structure was confirmed in Study 2, and the scale showed measurement invariance between sexes. IPASE scores were correlated with self-report and task measures of self-processing including self-concept clarity, self-consciousness, and self-esteem as well as measures of psychotic-like experiences. In Study 3, people with positive schizotypy had higher IPASE scores than a negative schizotypy and comparison group. In Study 4, people with schizophrenia had higher IPASE scores than healthy controls. Overall, the IPASE displayed strong psychometric qualities and is a brief alternative to resource-intensive phenomenological interviews in clinical, at-risk, and general population samples.