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Rasch Analysis of the 9-Item Shared Decision Making Questionnaire in Women With Breast Cancer

Wu, Tzu-Yi PhD; Chen, Cheng-Te PhD; Huang, Yi-Jing BS; Hou, Wen-Hsuan MD, PhD; Wang, Jung-Der ScD; Hsieh, Ching-Lin PhD

doi: 10.1097/NCC.0000000000000607
ARTICLES: ONLINE ONLY
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Background Shared decision making (SDM) is a best practice to help patients make optimal decisions by a process of healthcare, especially for women diagnosed with breast cancer and having heavy burden in long-term treatments. To promote successful SDM, it is crucial to assess the level of perceived involvement in SDM in women with breast cancer.

Objective The aims of this study were to apply Rasch analysis to examine the construct validity and person reliability of the 9-item Shared Decision Making Questionnaire (SDM-Q-9) in women with breast cancer.

Methods The construct validity of SDM-Q-9 was confirmed when the items fit the Rasch model's assumptions of unidimensionality: (1) infit and outfit mean square ranged from 0.6 to 1.4; (2) the unexplained variance of the first dimension of the principal component analysis was less than 20%. Person reliability was calculated.

Results A total of 212 participants were recruited in this study. Item 1 did not fit the model's assumptions and was deleted. The unidimensionality of the remaining 8 items (SDM-Q-8) was supported with good item fit (infit and outfit mean square ranging from 0.6 to 1.3) and very low unexplained variance of the first dimension (5.3%) of the principal component analysis. The person reliability of the SDM-Q-8 was 0.90.

Conclusions The SDM-Q-8 was unidimensional and had good person reliability in women with breast cancer.

Implications for Practice The SDM-Q-8 has shown its potential for assessing the level of perceived involvement in SDM in women with breast cancer for both research and clinical purposes.

Author Affiliations: Institute of Economics, Academia Sinica, Taipei (Dr Wu); Center for Teacher Education, National Tsing Hua University, Hsinchu (Dr Chen); School of Occupational Therapy, College of Medicine, National Taiwan University, Taipei (Ms Huang and Dr Hsieh); School of Gerontology Health Management and Master Program in Long-term Care, College of Nursing (Dr Hou), and Department of Physical Medicine and Rehabilitation, College of Medicine, School of Medicine (Dr Hou), Taipei Medical University; Department of Physical Medicine and Rehabilitation, Taipei Medical University Hospital (Dr Hou); Departments of Internal Medicine and Occupational and Environmental Medicine, National Cheng Kung University Hospital, Tainan (Dr Wang); Department of Public Health, College of Medicine, National Cheng Kung University, Tainan (Dr Wang); and Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei (Dr Hsieh), Taiwan.

This study was supported by research grants from the Taipei Medical University Aim for the Top University Project–Cancer Translational Center (TMUTOP103004-1) and the Ministry of Science and Technology (NSC-102-2314-B-038-007-MY3, MOST-105-2314-B-038-012, and MOST-106-2314-B-038-042). The sponsors were not involved in the study design; in the collection, analysis, and interpretation of the data; in the writing of the report; or in the decision to submit the paper for publication.

The authors have no conflicts of interest to disclose.

Correspondence: Wen-Hsuan Hou, MD, PhD, School of Gerontology Health Management and Master Program in Long-Term Care, 250 Wu-Hsing St, Taipei City, Taiwan (houwh@tmu.edu.tw).

Accepted for publication February 19, 2018.

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