78 | Chapter 3 The Dutch versions of the SDM-Q-9 and SDM-Q-Doc (Appendix A) have previously shown to be reliable instruments for investigating how SDM is perceived43-45. Both are nineitem, validated questionnaires that measure patients’ and surgeons’ perceived level of SDM on a six-point Likert scale, ranging from 0 (completely disagree) to 5 (completely agree). Scores can be summed up, averaged, and then rescaled into a percentage range from 0 (no perceived SDM) to 100 (highest level of perceived SDM). In addition, the validated Control Preference Scale (CPS) was used to assess patients’ preference for and perceived involvement in the decision-making process. The scale contains five decision-making related statements, with two describing an active role of the patient (patient-led), one a shared role (collaborative), and two a passive role of the patient (physician-led), which we reduced into three categories for analysis46, 47. We developed two customized CPS measures alongside Degner’s original: one to assess surgeons’ perception of patients’ preference and another to measure their own preference for patient involvement in decision-making. For objective assessment of the level of SDM, the validated Observing Patient Involvement (OPTION) scale was used. The original OPTION5 manual48, in which only healthcare providers are assessed, was not specific enough as SDM should also allow the patient and their caregivers to actively participate in conversation49. For this reason, we used the OPTIONmcc manual50 and adapted it for our study, the OPTIONmcc+ (Appendix B). Instead of scoring patients and caregivers from 0 (passive participation) to 2 (active participation), they were assessed similarly to the surgeons on a 5-point scale. The seven OPTION items were scored based on the general description in the manual wherein scores for surgeons range from 0 (no effort) to 4 (exemplary effort) and scores for patients and caregivers from 0 (passive participation) to 4 (very active participation). Before actual assessment of the consultations, two raters (SD and RT) performed a calibration session. Each scored ten randomly chosen consultations independently to discuss any discrepancies in OPTION-scores to reach consensus. The OPTION-scores (0-28) of both raters were summed, averaged and then rescaled into a percentage total score between zero and hundred50. There are no officially defined cutoff values to interpret the observed level of SDM, but some studies have used three categories34, 39: low (0-33.3%), moderate (33.3-66.6%), and high (66.6-100%), which we adopted. Statistical analysis Statistical analyses were performed using IBM SPSS Statistics 2751, with a significance level set at p < 0.05. Only consultations with both surgeon’s and patient’s questionnaires were included for analysis. Descriptive data were employed in accordance with the normal distribution of the data. Before analysis of the data, the two-way mixed interrater reliability, single measurement intra-class correlations coefficients (ICC) with a
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