Statistical analysis
Principles for calculating the sample size: no preliminary calculation of the required sample size was carried out. Statistical data analysis: nonparametric methods of descriptive statistics were used. The median and interquartile range (IQR) were determined; the geometric mean was used in the description of relative values over time. The data analysis was performed using the IBM SPSS STATISTICS v.22 statistical program package. To compare quantitative data, the Mann–Whitney U-test and the Kruskal–Wallis test were used depending on the number of groups being compared; Pearson’s χ2 test was used for categorical data. Spearman’s rank correlation coefficient was used to compare nonlinear indicators. The differences were considered significant at p<0.05.