Development of self-report measures of physical, mental, and emotional fatigability: the michigan fatigability index (MIFI).

Abstract

Purpose: To develop item banks and static short-forms for a patient reported outcome measure of perceived physical, mental, and emotional fatigability-the Michigan Fatigability Index (MIFI).

Methods: Building on earlier qualitative work, this study utilized cognitive interviews in samples representing the general adult population across the lifespan, people with multiple sclerosis (MS), or people with fibromyalgia (FM) to develop initial item pools. A nationwide cross-sectional survey study in MS and FM samples was used to field test items to develop item banks.

Results: Exploratory and confirmatory factors analyses indicated single underlying dimensions for each of the MIFI subdomains, and a graded response model (GRM) supported item fit of 42, 28, and 23 items to the physical, mental, and emotional fatigability items banks, respectively. Differential item functioning was not detected for age, condition (FM vs. MS), education level, ethnicity, race, or sex. Expert review and GRM calibration data was used to inform the selection of three 6-item short forms that assess physical, mental, and emotional fatigability and to program associated computer adaptive tests.

Conclusion: The MIFI shows initial evidence of good psychometric properties. Users can administer the MIFI as a static short form and efforts are underway to provide access to the measure as a computer adaptive test. T-Score scale conversion allows comparison of individual scores to a normative clinical sample with a wide range of fatigability.