The SDM-Q-9 (patient) and SDM-Q-Doc (doctor) measure the extent to which a shared decision making process occurred during a provider-patient consultation. Aim was to assess the psychometric characteristics of the Dutch versions of the questionnaires.
Method:
Participants were consecutive patients and their treating specialist at the departments of psychiatry, gynecology, oncology (breast cancer), and ophthalmology, in two medical centers. For construct validity we used the Control Preferences Scale (CPS, ranging from 1 'patient decides' to 5 'doctor decides') and relevant scales of the Ideal Patient Autonomy Scale (IPAS). We expected the Dutch versions of the questionnaires to show one factor, to result in the highest scores in those who indicated a shared decision process on the CPS, to correlate positively with the “Patient Should Decide” scale of the IPAS and to correlate negatively with the “Doctor Knows Best” IPAS scale.
Result:
Out of 151 patients approached, 101 completed the questionnaires (76% female) and N=84 completed all SDM-Q-9 items. Mean age was 53 years (SD=19). Reliability of the scale was high in both patients (alpha=0.83) and doctors (alpha=0.87). Deleting the last item of the scale (My doctor and I reached an agreement on how to proceed) would only slightly improve reliability (alphapatients=0.85; alphadoctors=0.88). Confirmatory factor analyses (complete patient versus doctor data) showed that a unitary model, with all nine items constituting a single factor, fit the data well (TLI and CFI>0.90; RMSEA<.08 in both patients and doctors).
SDM-Q-9 (patient) scores were associated with the CPS in the expected direction: 82 and 84 in those reporting CPS scores 2 (patient, taking doctor’s opinion into account) and 3 (shared); 71 and 39 in CPS scores 4 (doctor, taking patient’s opinion into account) and 5 (doctor). For doctors the scores were 79, 79, 70 and 42, thus a perception of a more shared process when the patient decided. Correlations between the SDM-Q-9 and IPAS scales were low.
Conclusion:
The Dutch version of the SDM-Q-9 and SDM-Q-Doc questionnaires seem acceptable to participants and to reflect a unidimensional construct, with good reliability. Demonstration of convergent validity was equivocal, especially when compared to the IPAS. Perceptions of doctors and patients of the process seem to differ.