Rasch Analysis, Dimensionality, and Scoring of the Neuropsychiatric Inventory Irritability and Aggression Subscales in Individuals With Traumatic Brain Injury

Abstract

Objectives To develop, for versions completed by individuals with traumatic brain injury (TBI) and an observer, a more precise metric for the Neuropsychiatric Inventory (NPI) Irritability and Aggression subscales using all behavioral item ratings for use with individuals with TBI and to address the dimensionality of the represented behavioral domains. Design Rasch and confirmatory factor analyses of retrospective baseline NPI data from 3 treatment studies. Setting Postacute rehabilitation clinic. Participants NPI records (N = 525) consisting of observer ratings (n = 287) and self-ratings (n = 238) by participants with complicated mild, moderate, or severe TBI at least 6 months postinjury. Interventions Not applicable. Main Outcome Measures Frequency and severity ratings from NPI Irritability/Lability and Agitation/Aggression subscales. Results Confirmatory factor analyses of both observer and participant ratings showed good fit for either a 1-factor or a 2-factor solution. Consistent with this, the Rasch model also fit the data well with aggression items indicating the more severe end of the construct and irritability items populating the milder end. Conclusions Irritability and aggression appear to represent different levels of severity of a single construct. The derived Rasch metric offers a measure of this construct based on responses to all specific items that is appropriate for parametric statistical analysis and may be useful in research and clinical assessments of individuals with TBI.