Psychometric validation of the Cognitive Abilities Screening Instrument using Rasch analysis in people with dementia

Abstract

This study aimed to examine unidimensionality of the Cognitive Abilities Screening Instrument (CASI) using Rasch analysis and estimate Rasch person reliability in people with dementia. CASI data of people with dementia was collected from medical records of one general hospital in northern Taiwan. A total of 506 people with dementia were recruited from the Department of Neurology. The confirmatory factor analysis was first conducted to verify the fitness of one-factor model of the CASI. Unidimensionality was confirmed through 2 assumptions: the infit and outfit mean square were 0.5 to 1.5, and residual variance of the first principal component in principal component analysis was ≤20%. Rasch person reliability was estimated after undimensionality was supported. The results of one-factor model had shown that the Comparative Fit Index = 0.99, Tucker Lewis Index = 0.99, Root Means Square Error of Approximation = 0.015, and Standardized Root Mean Square Residual = 0.067, representing a good fit to the model. Both the infit and outfit mean square were ranged 0.87 to 1.37 and 0.86 to 1.42, respectively, and low residual variance of the first principal component (12.3%). Rasch person reliability result of 0.58 was satisfactory. The person-item map indicated the difference between item difficulty and person ability was within the acceptable limits (0.22 logits). Differential Item Function was found between −0.48 to 0.44 logits for gender, indicating the CASI functioned similarly for both genders. The 46 items of the CASI showed a unidimensional construct. The CASI had been demonstrated as a valid and reliable screening tool for assessing overall cognitive function in people with dementia, capturing their cognitive functions effectively.