Babak Nejati
1, Chien-Chin Lin
2,3, Vida Imani
4, Maria Browall
5, Chung-Ying Lin
6, Anders Broström
5*, Amir H Pakpour
7,5* 
1 Hematology and Oncology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
2 Department of Laboratory Medicine and Division of Hematology, Department of Internal Medicine, National Taiwan University Hospital, Taipei, Taiwan
3 Graduate Institute of Clinical Medicine, National Taiwan University, Taipei, Taiwan
4 Pediatric Health Research Center, Tabriz University of Medical Sciences Tabriz, Iran
5 Department of Nursing, School of Health and Welfare, Jönköping University, Jönköping, Sweden
6 Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Hong Kong
7 Social Determinants of Health Research Center, Qazvin University of Medical Sciences, Qazvin, Iran
Abstract
Background: This study investigated the psychometric properties of the 9-Item Shared DecisionMaking Questionnaire (SDM-Q-9) and the 9-Item Shared Decision-Making Questionnaire–Physician version (SDM-Q-Doc) using comprehensive and thorough psychometric methods in an oncology setting. Methods: Cancer survivors (n=1783; 928 [52.05%] males) and physicians (n=154; 121[78.58%] males) participated in this study. Each cancer survivor completed the SDM-Q-9. Physicians completed the SDM-Q-Doc for each of their cancer patient. Confirmatory factor analysis (CFA) and Rasch model were used to test the psychometric properties of SDM-Q-9 and SDM-Q-Doc. Results: SDM-Q-9 and SDM-Q-Doc demonstrated unidimensional structure in CFA and Rasch model. In addition, the measurement invariance was supported for both SDM-Q-9 and SDM-QDoc across sex using the multigroup CFA. Rash analysis indicates no differential item functioning(DIF)across sex for all the SDM-Q-9 and SDM-Q-Doc items. SDM-Q-9 and SDM-Q-Doc were moderately correlated (r=0.41; P<0.001). Conclusion: SDM-Q-9 and SDM-Q-Doc are valid instruments to assess shared decision making in the oncology setting.