**2.2 Statistical analysis**

The data were processed using SPSS 13.0 for Windows. The results are presented as means ± standard deviations and confidence intervals of 95% for quantitative variables and as percentages for categorical variables. For comparison of continuous variables the t test comparison of independent means and chi-square test to compare categorical variables was used. Survival analysis was performed using the Kaplan-Meier curves; we used the cutoff points at 36 months (three years). We performed a Cox regression analysis to estimate the independent effects of potential predictors of survival that had been significant in univariate analysis. For all tests a significant level of 0.05 was set.
