Psychometric Properties of the 9-Item Shared Decision-Making Questionnaire (SDM-Q-9): Validation of the Italian Version in a Large Psychiatric Clinical Sample.

Objective: The nine-item Shared Decision-Making Questionnaire (SDM-Q-9) is one of the most frequently used tools for assessing patients' involvement in medical decision-making, but so far, it not been validated in Italian. We aimed to validate the Italian version of the SDM-Q-9 in a clinical sample of patients suffering from major psychiatric disorders.

Method: We involved 307 consecutive patients affected by major psychiatric disorders (including schizophrenia spectrum disorders, affective disorders and eating disorders) in a real-world outpatient clinical setting. Confirmatory Factor Analysis (CFA) was conducted to examine the latent structure of the SDM-Q-9. Cronbach's alpha and correlations between the SDM-Q-9 and the Observing Patient Involvement (OPTION) scale were calculated to measure internal consistency and convergent validity respectively.

Results: The final sample was made up of 289 participants (response rate 94.1%) who completed the assessment. CFA confirmed the unidimensional structure as in the original version (χ2/df= 1.69; CFI= 0.98; TLI= 0.97; RMSEA= 0.05; SRMR= 0.08). Internal consistency of the total scale was Cronbach's α = .86. Regarding construct validity, we found several correlations between the SDM-Q-9 and OPTION scale.

Conclusions: Our findings suggest that the Italian version of SDM-Q-9 performs well if compared to other languages validated versions, so it is a useful patient-centred measure to assess the involvement in medical decision-making (SDM) of patients from clinical samples from the Italian-speaking population.