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

Abstract

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, patientreported 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 4–6weeks 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).