The factor structure of the Zanarini Rating Scale for Borderline Personality Disorder: Exploratory Structural Equation Modelling and measurement invariance over time

Objectives There is a lack of independent longitudinal evidence on the factor structure and validity of the Zanarini Rating Scale for Borderline Personality Disorder (ZAN-BPD). This study aimed to investigate the dimensionality of ZAN-BPD and its conceptual consistency over time. Methods Adult BPD participants (n = 276) were recruited for a multicentre, two-arm randomised clinical trial with ZAN-BPD measured at baseline and follow up at 12, 24 and 52 weeks. The construct and stability of the ZAN-BPD across 52 weeks was examined through a measurement equivalence/invariance procedure via Exploratory Structural Equation Modelling. Results Factor analysis results showed that the ZAN-BPD had a bi-2 factor structure that was stable over 52 weeks with a general factor and two specific factors. Factor loadings for eight of the nine items were greater for the general factor than the two specific factors. Factor 1 contrasts externalising distress with internalising distress. Factor 2 contrasts depression and self-destruction with interpersonal anxiety and conflict. Conclusion ZAN-BPD is a conceptually and empirically valid measure of total BPD symptom severity in BPD patients over time suitable for use in clinical trials. Two factors related to the expression of distress and self-harm may be utilised as possible predictors of outcome.