Psychometric Evaluation of the Japanese 9-Item Shared Decision-Making Questionnaire and Its Association with Decision Conflict and Patient Factors in Japanese Primary Care

INTRODUCTION: This study aimed to verify the internal consistency and validity of the Japanese version of the 9-item Shared Decision-Making Questionnaire (SDM-Q-9) and investigate the association among patient factors, shared decision-making experienced by patients, and patients’ decision conflict during the treatment decision process in primary outpatient settings in Japan. METHODS: Patients who visited a primary care outpatient unit for the first time and completed the Japanese version of SDM-Q-9 and the Decisional Conflict Scale (DCS) immediately after consultation were included. The internal consistency of SDM-Q-9 was assessed using Cronbach’s alpha coefficient. Factor analysis and structural equation modeling were used to investigate structural construct validity. The relationship among patient-perceived experiences of shared decision-making, decision conflict, and patient factors was evaluated using correlation analysis. RESULTS: A total of 131 patients with chronic diseases (55.0% females, 28.2% aged ≥ 70 years) were included in this analysis. Cronbach’s alpha for the Japanese version of SDM-Q-9 was 0.917, indicating a high degree of internal consistency. Confirmatory factor analysis indicated that the Japanese version of SDM-Q-9 had a one-factor structure. Spearman’s rank correlation analysis indicated that the correlation between SDM-Q-9 and DCS was −0.577 (p < 0.05), indicating a significant inverse correlation and convergent validity. Older age was positively associated with perceived support of the physician in understanding all information. CONCLUSIONS: We confirmed that the Japanese version of SDM-Q-9 was both reliable and valid for use in Japanese primary care settings. In addition, we found a clear association between shared decision-making and decisional conflict of patients.