Objective: The test-retest reliability and the convergent validity of the Fatigue Impact Scale (FIS) were evaluated using secondary data from 54 persons with multiple sclerosis (MS).
Methods: This reliability and validity study used FIS data from before and after two control periods to evaluate test-retest reliability. Convergent validity of the FIS with the Fatigue Severity Scale and with subscales of the SF-36 Health Survey was evaluated using data collected before the first control period.
Results: No significant differences between before and after FIS measurements and intraclass correlation coefficients ranging from .68 to .85 indicate that the FIS has good test-retest reliability except for the physical subscale. The expected moderate correlations between the FIS and several subscales of the SF-36 support its convergent validity. In contrast, the unexpected low correlation between the FIS and Fatigue Severity Scale does not support convergent validity.
Conclusion: The FIS has adequate reliability and validity and is recommended to evaluate the effectiveness of fatigue management interventions such as energy conservation education for persons with MS.