Rasch analysis of the Behavioral Assessment Screening Tool (BAST) in chronic traumatic brain injury

The Behavioral Assessment Screening Tool (BAST) measures neurobehavioral symptoms in adults with traumatic brain injury (TBI). Exploratory Factor Analyses established five subscales: Negative Affect, Fatigue, Executive Function, Impulsivity, and Substance Abuse. In the current study, we assessed all the subscales except Substance Abuse using Rasch analysis following the Rasch Reporting Guidelines in Rehabilitation Research (RULER) framework. RULER identifies unidimensionality and fit statistics, item hierarchies, targeting, and symptom severity strata as areas of interest for Rasch analysis. The BAST displayed good unidimensionality with only one item from the Impulsivity scale exhibiting potential item misfit (MnSQ 1.40). However, removing this item resulted in a lower average domain measure (1.42 to -1.49) and higher standard error (0.34 to 0.43) so the item was retained. Items for each of the four subscales also ranged in difficulty (i.e. endorsement of symptom frequency) with more severe symptoms being endorsed in the Fatigue subscale and more mild symptoms being endorsed in the Impulsivity subscale. Though Negative Affect and Executive Function displayed appropriate targeting, the Fatigue and Impulsivity Subscales had larger average domain values (1.35 and -1.42) meaning that more items may need to be added to these subscales to capture differences across a wider range of symptom severity. The BAST displayed excellent reliability via item and person separation indices and distinct strata for each of the four subscales. Future work should use Rasch analysis in a larger, more representative sample, include more items for the Fatigue and Impulsivity subscale, and include the Substance Abuse subscale.