The aim of this study was to assess the psychometric properties and transcultural adaptation into Spanish of the Multidimensional Fatigue Inventory in fibromyalgia patients.
The Spanish version of the Multidimensional Fatigue Inventory (MFI-S) was translated and cognitively pretested following cross-cultural adaptation guidelines. Test-retest reliability, convergent validity, and operational qualities were evaluated in a total of 116 fibromyalgia patients. Convergent validity was assessed comparing MFI-S with a visual analogue scale for global fatigue.
The intra-class correlation coefficients varied from moderate to excellent (from 0.64 to 0.91) and the standard errors of the mean ranged from 0.5 to 1.1 points for the five MFI-S domains. The coefficient of repeatability was less than 2 standard deviations and the limits of agreement ranged from 2 to 4 points for the MFI-S domains. A weak to fair significant relationship was found between each MFI-S domain and the visual analogue scale (from 0.21 to 0.32). The mean time required to complete the MFI-S was 3.2±2.0 minutes. None of the patients needed external help to complete the MFI-S, and there were very few missing values.
The MFI-S developed in this study presents a good reliability and reasonable construct validity for Spanish fibromyalgia patients unaffected by cognitive dysfunction and severe depression. This questionnaire is quick, easy to administer and interpret.