- To compare average values between two independent groups U Mann-Whitney test was used (for e.g. to compare experimental group with the control one); Wilcoxon signed-rank test was used for paired samples (for e.g. to compare first measurement with final measurement for experimental group). Comparison of fractions was conducted using Pearson's chi-square test of independence and Z test. The 95% confidence intervals were calculated on the basis of normal approximation.