Dimensionality of nonmotor neurobehavioral impairments when observed in the natural contexts of ADL task performance.

OBJECTIVE To examine diverse nonmotor neurobehavioral impairments (NBIs) that impact activities of daily living (ADL) task performance and to verify if such impairments can be viewed as one dimension when evaluated in an ecologically-relevant context. METHODS Rasch analysis was performed on data from 206 individuals diagnosed with dementia or cerebral vascular accident (CVA) who had been scored on 50 standardized NBIs from the A-ONE Neurobehavioral Impairment scale, based on naturalistic observation of ADL task performance. Evaluation of mean square (MnSq) infit and outfit values and principal components analysis (PCA) of residuals were used to evaluate unidimensionality of the items. Two evaluations were implemented: (1) to evaluate if there is a single global dimension common for persons with either dementia or CVA, and (2) to evaluate if the 50 NBIs are unidimensional, but comprised of different diagnosis-specific global hierarchies (dementia, left CVA, and right CVA). RESULTS The PCA indicated that 56.8% of variance was explained by the global measure (Rasch factor) of NBIs, with 4.9% of the unexplained variance explained by the first contrast. Four items showed outfit misfit to the common hierarchy. Developing diagnosis-specific global hierarchies resulted in improved PCA results for all 3 diagnostic groups (Rasch factor = 79.2% to 85.5%; unexplained variance in first contrast = 1.7% to 3.4%) after removal of 2 to 3 misfitting items. CONCLUSIONS Nonmotor NBIs, when evaluated based on naturalistic performance of ADL, can be considered unidimensional, but the hierarchical structure of the dimension likely varies across diagnostic groups. Further study is needed with larger samples to verify these results.