Background In the assessment of patients with rheumatoid arthritis (RA) it is important to measure fatigue. The National Institutes of Health's Patient-Reported Outcomes Measurement Information System (PROMIS) initiative developed an item bank for measuring fatigue. This item bank was translated into Dutch-Flemish language according to the FACIT methodology.
Objectives The aim of current study was to validate the Dutch-Flemish translation of the PROMIS Fatigue item bank (DF-PROMIS-Fatigue) in Dutch and Flemish RA patients. This is the first validation study of the PROMIS Fatigue item bank in RA patients.
Methods 2030 RA patients (1370 Dutch and 660 Flemish RA patients) completed a paper-and-pencil or web-based survey, including the full DF-PROMIS-Fatigue (95 items, 5-point Likert scale). One-factor confirmatory factor analysis assessed unidimensionality. Item response theory (IRT) models evaluated the item characteristics of the item bank, to facilitate future development of a computer adaptive test (CAT). A graded item response model (GRM) was fitted and construct validity was studied. Ordinal regression models evaluated Differential Item Functioning (DIF) for e.g. language (Dutch-Flemish vs. English and Dutch vs. Flemish), to analyse cross-cultural validity.
Results The analyses support unidimensionality of the DF-PROMIS-Fatigue (CFI=0.996 and TLI=0.996). Only 45 out of 4465 (1%) item pairs were marked as possibly locally dependent. The data of the item bank fit the GRM, and showed good coverage across the fatigue continuum (threshold-parameters ranged from -3.8 to 5.8). The item bank showed good cross-cultural validity: none of the DF-PROMIS-Fatigue items showed DIF between Dutch and Flemish language. Furthermore, the item bank showed good reliability (Cronbach's alpha=0.993). Analyses of construct validity are in progress and will be presented at the conference.
Conclusions The results indicate that the items of the DF-PROMIS-Fatigue fit a GRM. The DF-PROMIS-Fatigue can be used to develop a CAT for measuring fatigue in Dutch and Flemish RA patients.
Disclosure of Interest None declared