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Minimal Clinically Important Difference for the Rasch Neuropsychiatric Inventory Irritability and Aggression Scale for Traumatic Brain Injury

  • James F. Malec
    Correspondence
    Corresponding author James F. Malec, PhD, ABPP-Cn, Rp, Professor and Research Director, Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine and Rehabilitation Hospital of Indiana, 355 W. 16th St., Indianapolis, IN 46202.
    Affiliations
    Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine, Indianapolis, IN

    Rehabilitation Hospital of Indiana, Indianapolis, IN

    Mayo Clinic, Rochester, MN
    Search for articles by this author
  • Flora M. Hammond
    Affiliations
    Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine, Indianapolis, IN

    Rehabilitation Hospital of Indiana, Indianapolis, IN
    Search for articles by this author
Published:September 13, 2017DOI:https://doi.org/10.1016/j.apmr.2017.06.038

      Highlights

      • A measure combining the Irritability/Lability and Agitation/Aggression subscales of the Neuropsychiatric Inventory (NPI) has been developed for use with individuals with traumatic brain injury (TBI).
      • The new measure (the Rasch NPI Irritability and Aggression Scale for TBI [NPI-TBI-IA]) was developed with Rasch analysis and includes responses to all specific items on these subscales.
      • The minimal clinically important difference (MCID) is the smallest change on a clinical measure that is associated with a meaningful perceived difference in an individual's condition, function, or quality of life.
      • We determined the MCID for this measure using distribution-based statistical methods and by anchoring the measure to Global Impression of Change Scales completed by individuals with TBI, their observers, and their physicians.
      • Our analysis suggests that the MCID for the NPI-TBI-IA is 0.5 SD and that a 1 SD change indicates a robust clinically important difference for both observer ratings and participant self-ratings.

      Abstract

      Objective

      To determine the minimal clinically important difference (MCID) for a Rasch measure derived from the Irritability/Lability and Agitation/Aggression subscales of the Neuropsychiatric Inventory (NPI)—the Rasch NPI Irritability and Aggression Scale for Traumatic Brain Injury (NPI-TBI-IA).

      Design

      Distribution-based statistical methods were applied to retrospective data to determine candidates for the MCID. These candidates were evaluated by anchoring the NPI-TBI-IA to Global Impression of Change (GIC) ratings by participants, significant others, and a supervising physician.

      Setting

      Postacute rehabilitation outpatient clinic.

      Participants

      274 cases with observer ratings; 232 cases with self-ratings by participants with moderate-severe TBI at least 6 months postinjury.

      Interventions

      Not applicable.

      Main Outcome Measure

      NPI-TBI-IA.

      Results

      For observer ratings on the NPI-TBI-IA, anchored comparisons found an improvement of 0.5 SD was associated with at least minimal general improvement on GIC by a significant majority (69%–80%); 0.5 SD improvement on participant NPI-TBI-IA self-ratings was also associated with at least minimal improvement on the GIC by a substantial majority (77%–83%). The percentage indicating significant global improvement did not increase markedly on most ratings at higher levels of improvement on the NPI-TBI-IA.

      Conclusions

      A 0.5 SD improvement on the NPI-TBI-IA indicates the MCID for both observer and participant ratings on this measure.

      Keywords

      List of abbreviations:

      AIMS (Amantadine Irritability Multisite Study), GIC (Global Impression of Change), MCID (minimal clinically important difference), NPI (Neuropsychiatric Inventory), NPI-TBI-IA (Rasch Neuropsychiatric Inventory Irritability and Aggression Scale for Traumatic Brain Injury), RCI (reliable change index), RCID (robust clinically important difference), TBI (traumatic brain injury)
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