Rasch analysis of the 9-item Shared Decision Making Questionnaire for women with breast cancer




Poster session 3


Tuesday 18 September 2018 - 12:30 to 14:00

All authors in correct order:

Hou W1, Wu T2, Huang T3, Hsu C4
1 Master Program in Long-Term Care and Gerontology Health Management, Department of Physical Medicine and Rehabilitation,Taipei Medical University, Cochrane Taiwan, Taiwan
2 Institute of Economics, Academia Sinica, Taiwan
3 School of Nursing, College of Nusing, Taipei Medical University and Cochrane Taiwan, Taiwan
4 Cochrane Taiwan, Taipei Medical University, Taiwan
Presenting author and contact person

Presenting author:

Tsai-Wei Huang

Contact person:

Abstract text
Background: Breast cancer, one of the most prevalent cancers in women, negatively affects women's survival and health-related quality of life. Women with breast cancer need to discuss treatment options with their doctors thoroughly in order to make optimal treatment decisions.

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 the SDM-Q-9 was confirmed when the items fit the Rasch model's assumptions of unidimensionality: (1) infit and outfit mean square (MNSQ) ranged from 0.6 to 1.4; (2) the unexplained variance of the first dimension of the principle component analysis (PCA) was < 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 MNSQ ranging from 0.6 to 1.3) and very low unexplained variance of the first dimension (5.3%) of the PCA. The person reliability of the SDM-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 shared decision-making in women with breast cancer for both research and clinical purposes.


Relevance to patients and consumers: 

Shared decision making (SDM) is an approach to help patients make optimal decisions by a process of medical consultations. During the SDM process, both patients and doctors engage in the decision making and communicate opinions on treatments before they agree on a preferred choice. As a result, the patients may have less anxiety about the treatment and also better treatment outcomes. To promote successful SDM, it is crucial to assess the level of perceived involvement in SDM in women with breast cancer.