Italian adaptation and psychometric validation of the Fatigue Impact Scale (FIS) and its modified versions in adults with multiple sclerosis: a Rasch analysis study

Purpose: Several outcome measures are available to assess the severity of fatigue in people with multiple sclerosis (MS). The aim of this study was to adapt the Italian version of the Fatigue Impact Scale (FIS-40) and its modified versions: a 21-item Modified scale (MFIS-21), its 5-item short version (MFIS-5), and an 8-item version for daily use (DFIS-8) and investigate their measurement properties through classical theory-test (CTT) and Rasch analysis (RA).