The self-administered version of the Amyotrophic Lateral Sclerosis Functional Rating Scale–Revised (ALSFRS-R) is used to monitor function and disease progression in individuals with amyotrophic lateral sclerosis (ALS). However, the performance of the self-administered ALSFRS-R has not been assessed using Rasch Measurement Theory. Therefore, the purpose of this study was to examine the psychometric properties of the self-administered ALSFRS-R using Rasch analysis.
Rasch analysis was performed on self-administered ALSFRS-R data from individuals with ALS across Canada. The following 6 aspects of Rasch analysis were examined using RUMM2030: fit via residuals and chi-square statistics, targeting via person-item threshold maps, dependency via item residual correlations, unidimensionality through principal components analysis of residuals, reliability via person separation index, and stability through differential item functioning analyses for sex, age, and language.
Analysis was performed on 122 participants (mean age: 52.9 years; 62.8% men). The overall scale demonstrated good fit, reliability, and stability; however, multidimensionality was found. To address this issue, items were divided into 3 subscales (bulbar, motor, and respiratory function), and Rasch analysis was performed for each subscale. The subscales demonstrated good fit, reliability, stability, and unidimensionality. However, there were still issues with item dependency for all subscale and targeting for bulbar and respiratory subscales.
The self-administered ALSFRS-R is reliable, internally valid, and stable across sex, age, and language subgroups; however, it is recommended that the ALSFRS-R be scored by subscale. Future studies can look at revising and/or adding items to tackle misfit, redundancy, and ceiling effects.
Self-administered measures are simple to administer and inexpensive. The self-administered ALSFRS-R was found to be psychometrically sound and can be used as a tool to monitor disease progression and function in ALS.