Continuous variables are expressed as mean ± SD or median plus (interquartile) as appropriate. Categorical variables are presented as absolute numbers and percentages. Comparisons of continuous variables were performed by Wilcoxon’s signed rank test for paired samples and the Mann-Whitney U test for unpaired samples; comparisons of categorical variables were performed by Fisher’s exact test. A two-tailed P value ≤ 0.05 was regarded as statistically significant. All data were processed using the Statistical Package for Social Sciences, version 20 (SPSS, Chicago, IL, USA).