Determining Reliable Change Using the Abbreviated Modified Fatiguae Impact Scale
Objectives: The aim of this study was to evaluate the psychometric properties of a brief fatigue scale and calculate clinically useful reliable change scores.
Methods: Fifty-nine relapsing-remitting MS patients completed the modified Fatigue Impact Scale-5 (MFIS-5) at baseline and a 10 week follow-up as part of a larger study examining treatment adherence. Test-retest reliability of baseline and 10-week composite scores were assessed using a single measures two-way random effects Analysis of Variance Intraclass Correlation (sICC) with absolute agreement. Reliable change scores at the .80 and .90 confidence intervals were calculated using the Jacobson and Truax reliable change formula.
Results: The MFIS-5 demonstrated good test-retest reliability (sICC=.75). Reliable change calculations indicated that 4 point differences on the MFIS-5 represent meaningful change at the .80 confidence interval. Differences of 6 points represent change at the .90 confidence interval.
Conclusions: Despite widespread fatigue in MS, no brief measures have been shown to reliably detect clinically meaningful change. Results provide evidence that the MFIS-5 can be used to reliably evaluate significant change in MS patients’ fatigue. Changes of ≥ 4 on the abbreviated fatigue measure represent a reliable and meaningful change. The MFIS-5 may be given at baseline and post-treatment to evaluate fatigue outcomes as part of empirically supported treatment protocols.