130 | Chapter 5 Statistical analyses All statistical analyses were performed with R version 4.3.3 in RStudio software. Descriptive statistics fitting the type and distribution of the data were calculated to summarize the characteristics of the sample. Between-group differences in patient and tumor characteristics were analyzed using chi-square tests, and an unpaired t-test for age. Differences in total decisional conflict scores, knowledge and patient-experienced SDM were analyzed using linear regression. If assumptions of homoscedasticity and normal residual distributions were violated, we used bootstrapped 95% confidence intervals (b=1000). Differences in proportion of patients with CSDC, at baseline as well as 6-month follow-up, were analyzed using binary logistic regression. All regression models included propensity score correction to adjust for case-mix differences. The propensity score was calculated using a logistic regression model with arm as the dependent variable and Age, TNM, Subsite, and Education as independent variables. Treatment was not used in the PS correction since treatment choice was decided after counseling. Unpaired t-tests were applied to compare physicians’ evaluation of SDM between usual care and intervention. A subgroup analysis of differences in knowledge between the control and intervention group was done using a Mann-Whitney U test. All secondary outcomes were considered exploratory and hence no multiple testing correction was applied. Ethics This study was conducted according to the principles of the Declaration of Helsinki32. The ethical review committee of the Maastricht University Medical Center assessed and approved this study (registration number IRBd22-023). Additionally, all other participating centers obtained approval from their respective Medical Ethics Review Committee.
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