Measurement properties of the 9-item Shared Decision Making Questionnaire (SDM-Q-9): A systematic psychometric review and meta-analysis

Background. 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. Purpose. We systematically reviewed and synthesized psychometric evidence of the SDM-Q-9. Data Sources. MEDLINE, Web of Science, PsycInfo, and CINAHL. Study Selection. 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. Data Extraction. Details on study design, sample characteristics, and any information on psychometric evidence were extracted. Data Synthesis. 83 studies were included, with 73 articles contributing evidence on validity, 46 on reliability, and 3 on fairness. We found a high amount of psychometric evidence on validity and reliability of the SDM-Q-9, interpreting the score as 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. Conclusions. The SDM-Q-9 is highly reliable and valid for the subjectively experienced level of SDM by the patient. Further research is needed on alternative interpretations, and on fairness of the measure.