Statistical analysis
Statistical analyses were performed using SPSS version 21. Firstly, the normal distributed data were described by mean ± standard deviation, and the median and quartile range were used for descriptive statistics for non-normally distributed data; Secondly, the difference test of grouped variables was carried out based on the research purpose. Normally distributed data were compared using independent student's T-test, and nonparametric U Mann–Whitney test was used for non-normally distributed data. Chi-square test or Fisher's test was used to compare categorical variables. Among the test results, 