Fatigue in Parkinson’s disease: measurement properties of a generic and a condition-specific rating scale

Context: High quality fatigue rating scales are needed to advance understanding of fatigue nd determine the efficacy of interventions. Several fatigue scales are used in Parkinson’s isease, but few have been tested using modern psychometric methodology (Rasch analysis).

Objectives: To examine the measuring properties of the generic Functional Assessment of hronic Illness Therapy - Fatigue (FACIT-F) scale and the condition-specific 16-item arkinson Fatigue Scale (PFS-16) using Rasch analysis.

Methods: Postal survey data (n=150; 47% women; mean age, 70) were Rasch analyzed. FS-16 scores were tested according both to the original polytomous and the suggested lternative dichotomized scoring methods.

Results: The PFS-16 showed overall Rasch model fit whereas the FACIT-F showed signs of isfit, which probably was due to a sleepiness-related item and mixing of ositively/negatively worded items. There was no differential tem functioning by disease uration but by fatigue status (greater likelihood of needing to sleep or rest during the day mong people classified as non-fatigued) in the PFS-16 and FACIT-F. However, this did not mpact total score based estimated person measures. Targeting and reliability (≥0.86) was ood, but the dichotomized PFS-16 showed compromised measurement precision. olytomous and dichotomized PFS-16 and FACIT-F scores identified 6, 3 and 4 statistically istinct sample strata, respectively.

Conclusion: We found general support for the measurement properties of both scales. owever, polytomous PFS-16 scores exhibited advantages compared to dichotomous PFS-16 nd FACIT-F scores. Dichotomization of item responses compromises measurement recision and ability to separate people, and should be avoided.