Professor and Chair, Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine, Chief Medical Officer, Rehabilitation Hospital of Indiana, Goodman Hall 4700, 355 W. 16th St., Indianapolis, IN 46202. Electronic address: Flora.hammond@rhin.com.
OBJECTIVE: 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 scales using all behavioral item ratings for use with individuals with TBI and address the dimensionality of the represented behavioral domains.
DESIGN: Rasch and confirmatory factor analyses of retrospective baseline NPI data from three treatment studies. SETTING: Postacute rehabilitation clinic. PARTICIPANTS: 287 cases with observer ratings; 238 cases with self-ratings by participants with complicated mild, moderate or severe TBI at least 6 months post-injury. MAIN OUTCOME MEASURE: 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 one-factor or two-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.