1.5 Statistical analysis
Continuous variables were presented as median (interquartile range, IQR) and compared with the Kruskal-Wallis test between different groups; categorical variables were presented as numbers (%), and comparisons between different groups were done by the χ² test or Fisher’s exact test. A two-sided α of less than 0.05 was considered statistically significant. Statistical analysis was done using SPSS statistical software version 19.0 (SPSS Inc., Chicago, IL, USA).