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. 2012;7(12):e52028.
doi: 10.1371/journal.pone.0052028. Epub 2012 Dec 14.

Are scores on English and French versions of the PHQ-9 comparable? An assessment of differential item functioning

Erin Arthurs  1 , Russell J Steele, Marie Hudson, Murray Baron, Brett D Thombs; (CSRG) Canadian Scleroderma Research Group
Collaborators, Affiliations

Are scores on English and French versions of the PHQ-9 comparable? An assessment of differential item functioning

Erin Arthurs et al. PLoS One. 2012.

Abstract

Background: Medical research increasingly utilizes patient-reported outcome measures administered and scored in different languages. In order to pool or compare outcomes from different language versions, instruments should be measurement equivalent across linguistic groups. The objective of this study was to examine the cross-language measurement equivalence of the Patient Health Questionnaire-9 (PHQ-9) between English- and French-speaking Canadian patients with systemic sclerosis (SSc).

Methods: The sample consisted of 739 English- and 221 French-speaking SSc patients. Multiple-Indicator Multiple-Cause (MIMIC) modeling was used to identify items displaying possible differential item functioning (DIF).

Results: A one-factor model for the PHQ-9 fit the data well in both English- and French-speaking samples. Statistically significant DIF was found for 3 of 9 items on the PHQ-9. However, the overall estimate in depression latent scores between English- and French-speaking respondents was not influenced substantively by DIF.

Conclusions: Although there were several PHQ-9 items with evidence of minor DIF, there was no evidence that these differences influenced overall scores meaningfully. The PHQ-9 can reasonably be used without adjustment in Canadian English- and French-speaking samples. Analyses assessing measurement equivalence should be routinely conducted prior to pooling data from English and French versions of patient-reported outcome measures.

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Conflict of interest statement

Competing Interests: Actelion Pharmaceuticals and Pfizer Inc. have provided unrestricted educational and research funds to the Canadian Scleroderma Research Group. The commercial funding that provides support to the CSRG does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials.

Figures

Figure 1
Figure 1. MIMIC model for Patient Health Questionnaire - 9 (PHQ-9).
The base Multiple-Indicator Multiple-Cause (MIMIC) model consists of a confirmatory factor model with the additional direct effect of group (language) on the latent depression factor serving to control for group differences on the level of the latent depression factor. For differential item functioning (DIF) analysis, the direct effect of group on PHQ-9 items is assessed for each item separately by regressing items, one at a time, on language, controlling for any differences in the overall level of the latent depression factor between groups.
See this image and copyright information in PMC

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