Statistical analysis
The data were prospectively collected in a computerized database, and then analyzed by Statistical Package for Social Sciences, version 22.0 (SPSS Inc., Chicago, III). All continuous variables were expressed as the mean ± standard deviations, and the differences were tested for significance using the Student t-test. The differences in categorical variables were tested for significance with the χ2 or Fisher exact test, as appropriate, and were presented as proportions unless stated otherwise. p < 0.05 was considered to be statistically significant in results.