Statistical Analysis
The statistical analyses were performed using SPSS version 18.0 (SPSS Inc, Chicago, IL) and 5% was the level of significance. Categorical variables are presented as fre- quencies and percentages, and continuous variables as means and standard deviations for normally distributed data, and medians and interquartile ranges for nonpara- metric data. Between-group differences for categorical variables were determined by c2 statistics or Fisher exact test, as appropriate, for normally distributed continuous variables by unpaired 2-sample t tests, and for nonpara- metric continuous variables by Mann–Whitney U test.