Rasch analysis of fatigue severity scale in patients with epilepsy

Area of Science:

• Neurology
• Psychometrics
• Clinical Assessment

Background:

• Fatigue is a common and debilitating symptom in patients with epilepsy.
• Validated tools are needed to accurately assess fatigue severity in this population.
• The Fatigue Severity Scale (FSS) is a commonly used measure, but its psychometric properties in epilepsy require evaluation.

Purpose of the Study:

• To validate the psychometric properties of the Fatigue Severity Scale (FSS) in patients with epilepsy using the Rasch model.
• To assess the unidimensionality, reliability, and targeting of the FSS in this specific patient group.

Main Methods:

• The Rasch rating scale model (RSM) was applied to data from 307 adult epilepsy patients.
• Unidimensionality was assessed using infit/outfit mean squares and principal component analysis of Rasch residuals.
• Reliability was evaluated through separation reliability estimates and ratios, with Differential Item Functioning (DIF) analyzed for gender.

Main Results:

• Mixed evidence was found regarding the FSS's fit to the Rasch model.
• Items 1 and 2 ("My motivation is lower when I am fatigued" and "Exercise brings on my fatigue") showed significant misfit.
• The overall psychometric properties of the nine-item FSS were considered fair in this epilepsy cohort.

Conclusions:

• The nine-item FSS demonstrates fair psychometric properties for assessing fatigue in epilepsy patients.
• A modified FSS, omitting items 1 and 2, is suggested for improved validity and reliability in this population.
• A validated fatigue scale is crucial for identifying and managing fatigue in patients with epilepsy and its comorbidities.