Statistical analysis
The software SPSS 24.0 was used for the data analysis. The median (range/lower quartile and upper quartile, M-Range/QL & QU) was used to describe its concentration and tendency of dispersion, since not all the quantitative data were shown as the normal distribution.
The Kruskal-Wallis H test was used for the comparison between multiple independent groups. The enumeration data were represented as rate or composition ratio and the chi-square test was applied for comparisons between groups. The binary non-conditional logistic regression with single factor and multi-factor analyses were conducted to check the influencing factors of related variables. The predominant factors from the single factor analysis were considered for the further multi-factor regression analysis. The forward stepwise regression method was also adopted in the present study and p values lower than 0.05 and 0.10 were used as criteria. The two-tailed test was applied in all the analyses and p<0.05 was considered significant. The p value for the comparison of two groups was modified to 0.017.