The minimally important difference for the Japanese version of the health assessment questionnaire in patients with rheumatoid arthritis in daily practice

Abstract

Objective: To validate the minimally important difference (MID) of physical function using the Japanese version of the Health Assessment Questionnaire (J-HAQ) in a cohort of rheumatoid arthritis (RA).

Methods: Patients who participated in a cohort study in both October 2008 and April 2009 were analyzed. Patients self-rated their change in overall status over 6 months using a 5-point Likert scale (“much better”, “somewhat better”, “same”, “somewhat worse”, or “much worse”). The MID for J-HAQ score was defined as the mean J-HAQ score change in patients who rated themselves “somewhat better”. An effect size (ES) of 0.2–0.5 was considered to be suitable for MID.

Results: A total of 4560 patients were analyzed. The mean (standard deviation [SD]) MID for J-HAQ score was −0.06 (0.29), corresponding to an ES of 0.08. As exploratory analysis, 1999 patients with a J-HAQ score ≥0.5 and 28-joint disease activity score (DAS28) ≥ 2.6 at baseline were assessed. The mean (SD) MID for J-HAQ score of these patients was 0.13 (0.01), corresponding to an ES of 0.21.

Conclusions: The MID for J-HAQ score was 0.13 in patients with baseline J-HAQ score ≥0.5 and DAS28 ≥ 2.6. The MID for J-HAQ score was influenced by disease status and functional disability.

Keywords:

• Functional disability
• Health assessment questionnaire
• Minimally important difference
• Patient-reported outcomes
• Rheumatoid arthritis

Acknowledgments

We thank all patients participating in this study. We appreciate all members of the Institute of Rheumatology of the Tokyo Women’s Medical University, Tokyo, Japan for their successful management of the IORRA cohort.

Conflict of interest

Ayako Nakajima has received an honorarium from the speaker bureaus of Astellas Pharma Inc., Bristol-Myers Squibb K.K., Chugai Pharmaceutical Co., LTD., Janssen Pharmaceutical K.K., Mitsubishi Tanabe Pharma Corporation, Ono Pharmaceutical CO., LTD., Pfizer Japan Inc., Takeda Pharmaceutical CO., LTD., and UCB Japan Co. Ltd. Hisashi Yamanaka has received an honorarium from the speaker bureaus of AbbVie, Chugai, Daiichi-Sankyo, Eisai, Mitsubishi-Tanabe, Pfizer, Takeda, and Teijin Pharma, and has received research grants from AbbVie, Asahikasei Pharma, Astellas, Bristol-Myers-Squibb, Chugai, Daiichi-Sankyo, Eisai, GlaxoSmithKline, Janssen, Mitsubishi-Tanabe, MSD, Nippon Kayaku, Pfizer, Santen, Taisho-Toyama, Takeda, and Teijin Pharma. The rest of the authors do not have any conflicts to declare.