Screening and assessing ideas and delusions of reference using a semi-structured interview scale: a validation study of the Ideas of Reference Interview Scale (IRIS) in early psychosis patients.

ABSTRACT

BACKGROUND: Ideas and delusions of reference (IOR/DOR) are an important but underrecognized research target. Difficulty in their reliable assessment has been a barrier. A screening and assessment tool incorporating a self-information processing framework, the Ideas of Reference Interview Scale (IRIS), was developed and validated in patients with early psychosis. METHODS: Comprehensive review of IOR/DOR phenomena in the literature and pilot interviews were conducted for scale item development. Self-referential themes were summarized into 15 items. A consecutive sample of 137 outpatients with early psychosis was interviewed using IRIS. Their IOR/DOR experiences were also rated independently by clinicians on the Scale for the Assessment of Positive Symptoms (SAPS) and self-rated using the IOR subscale on the Schizotypal Personality Questionnaire (SPQ). Inter-rater reliability of IRIS was examined in a subsample of 15 participants. RESULTS: IRIS demonstrated good internal consistency (Cronbach's alpha 0.80), inter-rater reliability (intraclass correlation coefficient 0.95), and divergent validity with other symptoms. IRIS correlated satisfactorily with the IOR/DOR item or subscale on SAPS and SPQ (Spearman's rho = 0.71 and 0.47, respectively). DISCUSSION: IRIS provided a reliable high-resolution tool for progressing single-symptom research into IOR/DOR, a potential target feature of schizophrenia. The scale allows future investigation into self-referential processing and detailed phenomenological comparison in different clinical, subclinical, and healthy populations.