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

Background And Purpose: Limited 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.

Methods: This 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).

Results: The measures were equivalent in measuring fatigue ( = 0.75, < .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.

Conclusion: The 8a has comparable psychometric properties to the 7a in this population. Future work is needed in larger, more diverse samples.