The development and validation of the Unidimensional Fatigue Impact Scale (U-FIS).
BACKGROUND
The multidimensional assessment of fatigue is complicated by the interrelation of its multiple causes and effects.


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


METHODS
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.


RESULTS
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.


CONCLUSIONS
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.
Meads
D M
DM
Galen Research, Manchester, United Kingdom.
Doward
L C
LC
McKenna
S P
SP
Fisk
J
J
Twiss
J
J
Eckert
B
B
D000328:Adult; D000368:Aged; D005221:Fatigue / Q000209:etiology / Q000503:physiopathology* / Q000523:psychology*; D005260:Female; D006801:Humans; D007407:Interviews as Topic; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications*; D011594:Psychometrics; D015203:Reproducibility of Results; D018434:Sickness Impact Profile; D055815:Young Adult