Statistical analysis
The SPSS software (Armonk, New York corporation, USA) was used for data analysis, and GraphPad Prism (version 6.0, San Diego, California, USA) was used to plot graphs. All data are expressed as the mean ± SD. The independent sample t-test was used to compare and analyse data between the two groups, with homogenous variance of the bivariate normal distribution. One-way analysis of variance was used to analyse the differences between the two groups. Normally distributed bivariate data were analysed using the Pearson correlation test, while non-normally distributed bivariate data were analysed using the Spearman correlation test. P values < 0.05 were considered statistically significant.