Measuring Fatigue in Older Adults With Joint Pain: Reliability and Validity Testing of the PROMIS Fatigue Short Forms

Abstract

Background and PurposeLimited literature exists regarding the psychometric properties of the Patient-Reported Outcome Measurement Information System (PROMIS) Fatigue Short Form 8a. This study compared the psychometric properties of the 8a to the established PROMIS Fatigue Short Form 7a.MethodsThis was a cross-sectional study of 31 older adults with joint pain. Equivalent forms reliability and a Rasch analysis explored reliability (equivalent forms, internal consistency), validity (unidimensionality, item INFIT/OUTFIT), and additional psychometrics (item mapping).ResultsThe measures were equivalent in measuring fatigue (r = 0.75, p < .001) with good internal consistency (α = .87−.92). Both were unidimensional. Even though the 8a had better fitting items, neither measure could differentiate low levels of fatigue.ConclusionThe 8a has comparable psychometric properties to the 7a in this population. Future work is needed in larger, more diverse samples.