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Mult Scler. 2009 Oct;15(10):1228-38. doi: 10.1177/1352458509106714. Epub 2009 Jun 25.

The development and validation of the Unidimensional Fatigue Impact Scale (U-FIS).

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  • 1Galen Research, Manchester, United Kingdom.



The multidimensional assessment of fatigue is complicated by the interrelation of its multiple causes and effects.


The purpose of the research was to develop a unidimensional assessment of fatigue (U-FIS).


Data collected with the Fatigue Impact Scale (FIS) were subjected to Rasch analysis to identify potential problems with the scale. Additional items for the U-FIS were generated from interviews with UK MS patients. The U-FIS was tested for face and content validity in patient interviews and included in a validation survey to determine dimensionality (Rasch model), reliability and validity.


The original FIS was not unidimensional when subscale items were combined. The modification of the FIS and addition of a number of items allowed the development of a 22-item unidimensional scale (U-FIS) that was reliable (Cronbach Alpha = 0.96; test-retest = 0.86,) and valid given correlations with the Nottingham Health Profile and ability to distinguish between MS severity groups. There was no significant difference in U-FIS scores according to MS type.


It is valid to conceptualize the functional impact of fatigue as unidimensional. The U-FIS is a reliable and valid questionnaire that will allow the measurement of this construct in clinical studies.

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