Measurement Properties of the 9-Item Shared Decision Making Questionnaire (SDM-Q-9)

Abstract: The 9-item Shared Decision Making Questionnaire (SDM-Q-9) is widely used to measure shared decision-making (SDM) across clinical settings, but no study so far has synthesized its psychometric properties. In the present study, we systematically reviewed and synthesized psychometric evidence on the SDM-Q-9. The MEDLINE, Web of Science, PsycInfo, and CINAHL databases were searched for original studies in English or German, providing any information on psychometric properties of the SDM-Q-9 considering all possible interpretations and constructs measured by the instrument. Details on study design, sample characteristics, and information on psychometric evidence were extracted. We included 101 studies, with 49 articles contributing evidence on reliability, 91 on validity (87 on interrelations with other variables and 68 on the internal structure), and three on fairness. We found a high amount of psychometric evidence on the validity and reliability of the SDM-Q-9 as a measure of SDM perceived by the patient. Evidence is lacking for other interpretations and fairness. Notable is the weak association of the SDM-Q-9 with physician-rated SDM. In summary, substantial evidence supports reliability and validity of the SDM-Q-9 for assessing the subjectively experienced level of SDM by the patient, but further research is needed on alternative interpretations and on fairness of the measure.