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Supplementary Material for: A Common Metric for Self-Reported Severity of Personality Disorder

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posted on 25.05.2020, 08:00 by Zimmermann J., Müller S., Bach B., Hutsebaut J., Hummelen B., Fischer F.
Introduction: Dimensional models of personality disorders (PD) in the DSM-5 and ICD-11 share a focus on impairments in self and interpersonal functioning to represent the general features and severity of PD. This new perspective has led to the development of numerous measures for assessing individual differences in PD severity. While this improves choices for researchers and practitioners, it also poses the challenge of an increasing lack of standardization. Objective: The aim of this study is to establish a common metric across 6 widely used self-report measures of PD severity using item response theory models. Methods: 849 participants completed a survey including the Inventory of Personality Organization – 16-item version (IPO-16), the Level of Personality Functioning Scale – Brief Form 2.0, the Level of Personality Functioning Scale – Self-Report, the Operationalized Psychodynamic Diagnosis – Structure Questionnaire Short Form, the Personality Inventory for DSM-5 – Brief Form Plus and the Standardized Assessment of Severity of Personality Disorder (SASPD). We fitted exploratory multidimensional graded response models and used bifactor rotation to extract a general factor across measures. Factor scores were linked to representative T scores using data from a representative survey of 2,502 participants who completed the IPO-16. Results: When using bifactor rotation in a 7-factor model, all items loaded positively on the general factor, and the general factor explained 65.5% of the common variance. With the exception of the SASPD, all measures provided highly discriminating items (factor loadings >0.70) for measuring the general factor and reached an acceptable reliability (>0.80) across a wide range of the latent continuum. We constructed a crosswalk table linking total scores of the 6 measures to each other and to representative T scores. Conclusions: Our results suggest that 6 different self-report measures of the severity of PD capture a strong common factor and can therefore be scaled along a single latent continuum. Our results may facilitate instrument-independent assessment of severity of PD and increase comparability across studies.