James F Malec1, Flora M Hammond2. 1. Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine, Indianapolis, IN; Rehabilitation Hospital of Indiana, Indianapolis, IN; Mayo Clinic, Rochester, MN. Electronic address: jfmalec@iupui.edu. 2. Department of Physical Medicine and Rehabilitation, Indiana University School of Medicine, Indianapolis, IN; Rehabilitation Hospital of Indiana, Indianapolis, IN.
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.
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.