J Rheumatol 2015 Mar 15;42(3):413-20. Epub 2015 Jan 15.
From the Arthritis Center Twente; the Department of Psychology, Health and Technology, and the Department of Research Methodology, Measurement and Data Analysis, University of Twente; Department of Rheumatology and Clinical Immunology, Medical Spectrum Twente, Enschede; Department of Rheumatic Diseases, Radboud University Medical Centre, Nijmegen; and the Department of Rheumatic Diseases, Meander Medisch Centrum, Amersfoort, the Netherlands.M.A.H. Oude Voshaar, Postdoctoral Researcher, MSc; P.M. ten Klooster, Assistant Professor, PhD; C.B. Bode, Assistant Professor, PhD; Arthritis Center Twente, and the Department of Psychology, Health and Technology, University of Twente; H.E. Vonkeman, Rheumatologist, Assistant Professor, MD, PhD; M.A.F.J. van de Laar, Rheumatologist, Full Professor, MD, PhD; Arthritis Center Twente, and the Department of Psychology, Health and Technology, University of Twente, and the Department of Rheumatology and Clinical Immunology, Medical Spectrum Twente; C.A.W. Glas, Full Professor, PhD; Department of Research Methodology, Measurement and Data Analysis, University of Twente; T. Jansen, Rheumatologist, MD, PhD; P.L.C.M. van Riel, Rheumatologist, Full Professor, MD, PhD; Department of Rheumatic Diseases, Radboud University Medical Centre; I. van Albada-Kuipers, Rheumatologist, MD; Department of Rheumatic Diseases, Meander Medisch Centrum.
Objective: To compare the psychometric functioning of multidimensional disease-specific, multiitem generic, and single-item measures of fatigue in patients with rheumatoid arthritis (RA).
Methods: Confirmatory factor analysis (CFA) and longitudinal item response theory (IRT) modeling were used to evaluate the measurement structure and local reliability of the Bristol RA Fatigue Multi-Dimensional Questionnaire (BRAF-MDQ), the Medical Outcomes Study Short Form-36 (SF-36) vitality scale, and the BRAF Numerical Rating Scales (BRAF-NRS) in a sample of 588 patients with RA.
Results: A 1-factor CFA model yielded a similar fit to a 5-factor model with subscale-specific dimensions, and the items from the different instruments adequately fit the IRT model, suggesting essential unidimensionality in measurement. The SF-36 vitality scale outperformed the BRAF-MDQ at lower levels of fatigue, but was less precise at moderate to higher levels of fatigue. At these levels of fatigue, the living, cognition, and emotion subscales of the BRAF-MDQ provide additional precision. The BRAF-NRS showed a limited measurement range with its highest precision centered on average levels of fatigue.
Conclusion: The different instruments appear to access a common underlying domain of fatigue severity, but differ considerably in their measurement precision along the continuum. The SF-36 vitality scale can be used to measure fatigue severity in samples with relatively mild fatigue. For samples expected to have higher levels of fatigue, the multidimensional BRAF-MDQ appears to be a better choice. The BRAF-NRS are not recommended if precise assessment is required, for instance in longitudinal settings.