Data analysis
The data collected were statistically analyzed by the statistical
computer software SPSS, version 15.0. A post hoc analysis of
temporal trend was performed. Descriptive statistics were calculated for
all demographic and clinical variables. Continuous variables were
presented as mean and standard deviation (SD), and categorical variables
as frequency and percentage. The normality assumption was verified using
the Shapiro-Wilk test. T-student and χ2 tests were
adopted for comparisons between categorical variables. T-test and
non-parametric Mann-Whitney tests were adopted for comparisons between
continuous variables. Kaplan-Meier curves estimated the survival
function. Statistical significance was set at levels of P <
0.05.