2.2 Statistical analysis
Continuous data are expressed as the mean ± standard deviation and their differences were evaluated using Student’s t -test. For categorical data, the differences were evaluated using the χ2 and Fisher exact tests. Time-to-event analyses were performed using Kaplan–Meier estimates and compared between groups using the log-rank test. Independent predictors of overall survival were determined using Cox regression analysis. The multivariable models included covariates with a p <0.10 in the univariate analyses. All statistical analyses were performed using StatView version 5.0 software (SAS Institute, Cary, NC). In each analysis, p <0.05 was regarded as significant.
RESULTS