Psychometric properties of a short version of Lee Fatigue Scale used as a generic PROM in persons with stroke or osteoarthritis: assessment using a Rasch analysis approach

Background: Fatigue is a common symptom associated with a wide range of diseases and needs to be more thoroughly studied. To minimise patient burden and to enhance response rates in research studies, patient-reported outcome measures (PROM) need to be as short as possible, without sacrificing reliability and validity. It is also important to have a generic measure that can be used for comparisons across different patient populations. Thus, the aim of this secondary analysis was to evaluate the psychometric properties of the Norwegian 5-item version of the Lee Fatigue Scale (LFS) in two distinct patient populations.

Methods: The sample was obtained from two different Norwegian studies and included patients 4-6 weeks after stroke (n = 322) and patients with osteoarthritis on a waiting list for total knee arthroplasty (n = 203). Fatigue severity was rated by five items from the Norwegian version of the LFS, rating each item on a numeric rating scale from 1 to 10. Rasch analysis was used to evaluate the psychometric properties of the 5-item scale across the two patient samples.

Results: Three of the five LFS items ("tired", "fatigued" and "worn out") showed acceptable internal scale validity as they met the set criterion for goodness-of-fit after removal of two items with unacceptable goodness-of-fit to the Rasch model. The 3-item LFS explained 81.6% of the variance, demonstrated acceptable unidimensionality, could separate the fatigue responses into three distinct severity groups and had no differential functioning with regard to disease group. The 3-item version of the LFS had a higher separation index and better internal consistency reliability than the 5-item version.

Conclusions: A 3-item version of the LFS demonstrated acceptable psychometric properties in two distinct samples of patients, suggesting it may be useful as a brief generic measure of fatigue severity.

Trial registration: Clinicaltrials.gov: NCT02338869; registered 10/04/2014 (stroke study).