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. 2014 Mar 17;9(3):e91979.
doi: 10.1371/journal.pone.0091979. eCollection 2014.

The comparability of English, French and Dutch scores on the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F): an assessment of differential item functioning in patients with systemic sclerosis

Linda Kwakkenbos  1 , Linda M Willems  2 , Murray Baron  3 , Marie Hudson  3 , David Cella  4 , Cornelia H M van den Ende  2 , Brett D Thombs  5 ; Canadian Scleroderma Research Group
Collaborators, Affiliations

The comparability of English, French and Dutch scores on the Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F): an assessment of differential item functioning in patients with systemic sclerosis

Linda Kwakkenbos et al. PLoS One. .

Abstract

Objective: The Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-F) is commonly used to assess fatigue in rheumatic diseases, and has shown to discriminate better across levels of the fatigue spectrum than other commonly used measures. The aim of this study was to assess the cross-language measurement equivalence of the English, French, and Dutch versions of the FACIT-F in systemic sclerosis (SSc) patients.

Methods: The FACIT-F was completed by 871 English-speaking Canadian, 238 French-speaking Canadian and 230 Dutch SSc patients. Confirmatory factor analysis was used to assess the factor structure in the three samples. The Multiple-Indicator Multiple-Cause (MIMIC) model was utilized to assess differential item functioning (DIF), comparing English versus French and versus Dutch patient responses separately.

Results: A unidimensional factor model showed good fit in all samples. Comparing French versus English patients, statistically significant, but small-magnitude DIF was found for 3 of 13 items. French patients had 0.04 of a standard deviation (SD) lower latent fatigue scores than English patients and there was an increase of only 0.03 SD after accounting for DIF. For the Dutch versus English comparison, 4 items showed small, but statistically significant, DIF. Dutch patients had 0.20 SD lower latent fatigue scores than English patients. After correcting for DIF, there was a reduction of 0.16 SD in this difference.

Conclusions: There was statistically significant DIF in several items, but the overall effect on fatigue scores was minimal. English, French and Dutch versions of the FACIT-F can be reasonably treated as having equivalent scoring metrics.

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Conflict of interest statement

Competing Interests: We would like to confirm that co-author Dr. Brett D. Thombs is a PLOS ONE Editorial Board Member. This does not alter our adherence to PLOS ONE Editorial policies and criteria. We have the following interests. INOVA Diagnostics Inc. (San Diego, CA), Dr. Fooke Laboratorien GmbH (Neuss, Germany), Euroimmun (Lubeck, Germany), Mikrogen GmbH (Neuried, Germany), Pfizer and Actelion pharmaceuticals have provided unrestricted educational and research funds to the Canadian Scleroderma Research Group. There are no patents, products in development or marketed products to declare. This does not alter our adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors.

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