2.5. Statistical Analysis

Fisher’s test was used to test categorical variables. Kolmogorov–Smirnov test was used to test normality, and the unpaired Student’s t-test or Mann–Whitney U test was used for continuous variables. A p value < 0.05 was considered statistically significant. Overall survival was evaluated using the Kaplan–Meier curve, and a comparison between groups was evaluated using the log-rank test as univariate analysis. For the multivariate analysis, a Cox proportional hazard model was used. The best cut-off values in receiver operating characteristic (ROC) analysis were determined by the Youden index. All statistical analyses were performed using Easy R (EZR) version 1.29 (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (the R Foundation for Statistical Computing, Vienna, Austria) [24].