title: The PROMIS fatigue item bank has good measurement properties in patients with fibromyalgia and severe fatigue.
abstract: Efficient management of fibromyalgia (FM) requires precise measurement of FM-specific symptoms. Our objective was to assess the measurement properties of the Patient-Reported Outcome Measurement Information System (PROMIS) fatigue item bank (FIB) in people with FM.
  
  
  
  We applied classical psychometric and item response theory methods to cross-sectional PROMIS-FIB data from two samples. Data on the clinical FM sample were obtained at a tertiary medical center. Data for the U.S. general population sample were obtained from the PROMIS network. The full 95-item bank was administered to both samples. We investigated dimensionality of the item bank in both samples by separately fitting a bifactor model with two group factors; experience and impact. We assessed measurement invariance between samples, and we explored an alternate factor structure with the normative sample and subsequently confirmed that structure in the clinical sample. Finally, we assessed whether reporting FM subdomain scores added value over reporting a single total score.
  
  
  
  The item bank was dominated by a general fatigue factor. The fit of the initial bifactor model and evidence of measurement invariance indicated that the same constructs were measured across the samples. An alternative bifactor model with three group factors demonstrated slightly improved fit. Subdomain scores add value over a total score.
  
  
  
  We demonstrated that the PROMIS-FIB is appropriate for measuring fatigue in clinical samples of FM patients. The construct can be presented by a single score; however, subdomain scores for the three group factors identified in the alternative model may also be reported.
authors.affiliation: Department of Health Sciences Research, Mayo Clinic, Rochester, MN, USA. Yost.Kathleen@mayo.edu.|Kern Center for the Science of Health Care Delivery, Mayo Clinic, Rochester, MN, USA. Yost.Kathleen@mayo.edu.
authors.forename: Kathleen J
authors.initials: KJ
authors.lastname: Yost
authors.affiliation: Department of Psychology, University of Minnesota, Minneapolis, MN, USA.
authors.forename: Niels G
authors.initials: NG
authors.lastname: Waller
authors.affiliation: Kern Center for the Science of Health Care Delivery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Minji K
authors.initials: MK
authors.lastname: Lee
authors.affiliation: Department of General Internal Medicine, Mayo Clinic, Rochester, MN, USA.
authors.forename: Ann
authors.initials: A
authors.lastname: Vincent
mesh_terms: D003430:Cross-Sectional Studies; D005221:Fatigue / Q000503:physiopathology*; D005260:Female; D005356:Fibromyalgia / Q000503:physiopathology* / Q000628:therapy*; D006801:Humans; D007256:Information Systems; D008297:Male; D008875:Middle Aged; D000071066:Patient Reported Outcome Measures; D011594:Psychometrics / Q000379:methods; D011788:Quality of Life
keywords: Fatigue; Fibromyalgia; Item response theory; Patient-Reported Outcome Measurement Information System (PROMIS)