Validity and reliability of the 9-item Shared Decision Making Questionnaire (SDM-Q-9) in a national survey in Hungary

BACKGROUND: The nine-item Shared Decision Making Questionnaire (SDM-Q-9) is one of the most frequently applied instruments for assessing patients’ involvement in medical decision-making. Our objectives were to develop a Hungarian version of SDM-Q-9, to evaluate its psychometric properties and to compare its performance between primary and specialised care settings. METHODS: In 2019, a sample of adults (n = 537) representative of the Hungarian general population in terms of age, gender and geographic region completed an online survey with respect to a recent health-related decision. Outcome measures included SDM-Q-9 and Control Preferences Scale-post (CPS(post)). Item characteristics, internal consistency reliability and the factor structure of SDM-Q-9 were determined. RESULTS: The overall ceiling and floor effects for SDM-Q-9 total scores were 12.3% and 2.2%, respectively. An excellent internal consistency reliability (Cronbach’s alpha 0.925) was demonstrated. Exploratory factor analysis resulted in a one-factor model explaining 63.5% of the variance of SDM-Q-9. A confirmatory factor analysis supported the acceptability of this model. Known-groups validity was confirmed with CPS(post) categories; mean SDM-Q-9 total scores were higher in the ‘Shared decision’ category (72.6) compared to both ‘Physician decided’ (55.1, p = 0.0002) and ‘Patient decided’ (57.2, p = 0.0086) categories. In most aspects of validity and reliability, there was no statistically significant difference between primary and specialised care. CONCLUSIONS: The overall good measurement properties of the Hungarian SDM-Q-9 make the questionnaire suitable for use in both primary and specialised care settings. SDM-Q-9 may be useful for health policies targeting the implementation of shared decision-making and aiming to improve efficiency and quality of care in Hungary.