2.4. Statistical analysis

Pearson Chi-square test, or Fisher’s exact test if necessary, was used to compare the categorical variables between the SBBC and MBBC. Survival outcomes of different groups were estimated by Kaplan-Meier curves and compared by log-rank test. In multivariate analyses, cox proportional hazards models were conducted to evaluate the association between survival outcomes and potential prognostic factors based on hazard ratios (HRs) and 95% confidential interval (CI). For all statistical analyses, a p value of less than 0.05 was defined as statistically significant. All data analyses were performed using SPSS version 26.0 (SPSS, Chicago, Illinois, USA) and R version 3.6.2 (R Foundation for Statistical Computing).