2.9. Statistical Analysis
Nelson, T1–T3, death, CRC
REGRESSION, NELSON, INTERACTION
All participants were randomized and those whose sCD40L levels in residual serum samples could be measured were included in this analysis. Categorical and continuous variables in the vitamin D and placebo groups were compared using chi-squared and Mann–Whitney tests, respectively. The serum sCD40L levels were divided into tertiles (T1–T3), and chi-square and Kruskal–Wallis tests were employed to compare categorical and continuous variables among sCD40L tertiles, considering the non-normally distributed nature of the data and the need to assess differences among more than three groups. For survival analyses, 5-year RFS rates were compared among tertiles and between vitamin D and placebo groups. Moreover, Nelson–Aalen cumulative hazard curves were created to show the changes in relapse or death risk over time. Hazard ratios (HRs) and corresponding 95% confidence intervals (CIs) were computed utilizing a Cox proportional hazard model. Interaction tests based on a Cox regression model were conducted to discern any potential divergence in the effects of vitamin D supplementation across the tertiles of serum sCD40L levels. Two-way interaction tests were employed to compare the subgroup featuring the highest tertile of serum sCD40L among CRC patients with the remaining participants. Statistical significance was indicated by two-sided 