Statistical methods
Statistical analysis was performed by SPSS 24.0 system software (SPSS, USA). All analyses were conducted according to the intention-to-treat principle. Count data were expressed as constituent ratio and the chi-square test was used for comparison. Continuous variables were expressed as the mean ± standard deviation (SD), non-normally distributed data were presented as median with interquartile range (IQR). The t-test was used for the comparison of normally distributed continuous variables, while the Mann-Whitney U test was applied for the comparison of non-normally distributed continuous variables. An independent samples t-test was used on variables of the two groups compared. 