Spss statistical software for windows ver 18.0

Comparisons between categorical variables were performed using Pearson’s χ² test or Fisher’s exact test where appropriate. Continuous variables were compared using Student’s t test (when values were normally distributed) or the Mann-Whitney test (when the values had a distribution that departed significantly from normal). Survival analysis was performed using the Kaplan-Meier method and comparison were made using the log-rank test. Univariate and multivariate analyses using Cox’s proportional hazard models were performed to evaluate the prognostic factors. The correlation between two variables was examined by Pearson’s correlation analysis (when the variables were normally distributed) or Spearman’s correlation analysis (when the variables had a distribution that departed significantly from normal). A value of P < 0.05 was considered statistically significant. All data were analyzed using SPSS statistical software for Windows (ver. 18.0; SPSS Inc., Chicago, IL, United States).
All continuous variable data were expressed as mean ± standard error (when the values were normally distributed) or medians (range) (when the values had a distribution that departed significantly from normal). All data regarding categorical variables are shown as n (proportion).