Assessment of differential item functioning of the PHQ-9, HADS-D and PROMIS-depression scales in persons with and without multiple sclerosis.

We tested for the presence of differential item functioning (DIF) in commonly used measures of depressive symptoms, in people with multiple sclerosis (MS) versus people with a psychiatric disorder without MS. Participants included individuals with MS, or with a lifetime history of a depressive or anxiety disorder (Dep/Anx) but no immune-mediated inflammatory disease. Participants completed the Patient Health Questionnaire (PHQ-9), Hospital Anxiety and Depression Scale (HADS), and the Patient Reported Outcome Measurement Information System (PROMIS)-Depression. We assessed unidimensionality of the measures using factor analysis. We evaluated DIF using logistic regression, with and without adjustment for age, gender and body mass index (BMI). We included 555 participants (MS: 252, Dep/Anx: 303). Factor analysis showed that each depression symptom measure had acceptable evidence of unidimensionality. In unadjusted analyses comparing the MS versus Dep/Anx groups we identified multiple items with evidence of DIF, but few items showed DIF effects that were large enough to be clinically meaningful. We observed non-uniform DIF for one PHQ-9 item, and three HADS-D items. We also observed DIF with respect to gender (one HADS-D item), and BMI (one PHQ-9 item). For the MS versus Dep/Anx groups, we no longer observed DIF post-adjustment for age, gender and BMI. On unadjusted and adjusted analyses, we did not observe DIF for any PROMIS-D item. Our findings suggest that DIF exists for the PHQ-9 and HADS-D with respect to gender and BMI in clinical samples that include people with MS whereas DIF was not observed for the PROMIS-Depression scale.

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Déclaration de conflit d'intérêts

Declaration of Competing Interest All authors have completed the Unified Competing Interest form at http://www.icmje.org/coi_disclosure.pdf and declare that Ruth Ann Marrie, Lesley Graff, Amber Salter, James Marriott and Charles Bernstein have relationships that could be perceived to constitute a conflict of interest, and all authors have non-financial interests (research funding from government or non-profit sources that may be relevant to the submitted work. Ruth Ann Marrie receives research funding from: CIHR, Research Manitoba, Multiple Sclerosis Society of Canada, Multiple Sclerosis Scientific Foundation, Crohn's and Colitis Canada, National Multiple Sclerosis Society, CMSC, the Arthritis Society and US Department of Defense. She is a co-investigator on a study funded in part by Biogen Idec and Roche (no funds to her/her institution). She is supported by the Waugh Family Chair in Multiple Sclerosis. Lisa Lix receives research funds from CIHR, NSERC, and the Arthritis Society. James Bolton receives research funding from CIHR, Brain and Behavior Research Foundation and the MS Society of Canada. John Fisk receives research funds from CIHR, the MS Society of Canada, Crohn's and Colitis Canada, Research Nova Scotia; consultation and distribution royalties from MAPI Research Trust. Kathryn Fitzgerald receives research funds from NIH, CMSC, US Department of Defense and National MS Society. Lesley Graff receives research funds from CIHR, and Crohn's and Colitis Canada and has consulted to Roche Canada. Carol Hitchon has research funds for unrelated studies from UCB Canada and Pfizer. Kaarina Kowalec receives research funds from the CMSC, US Department of Defense, CIHR, NIH. James Marriott has conducted clinical trials for Biogen Idec and Roche, and receives research funding from the MS Society of Canada. Scott Patten receives research funding from CIHR, the MS Society of Canada, Roche, Biogen and the Government of Alberta. Amber Salter receives research funding from Multiple Sclerosis Society of Canada, National Multiple Sclerosis Society, CMSC and the US Department of Defense. Charles Bernstein has consulted to Abbvie Canada, Amgen Canada, BMS Canada, JAMP Canada, Janssen Canada, Pfizer Canada, Roche Canada, Sandoz Canada, Takeda Canada, and has received unrestricted educational grants from Abbvie Canada, BMS Canada, Janssen Canada, Pfizer Canada and Takeda Canada. He has been on speaker's bureaus of Abbvie Canada and Shire Canada.