2.6. Statistical Analysis

The normality of the distribution and the homogeneity of variable variances were conducted in the experimental groups using the Shapiro-Wilk test and Levene’s test, respectively. In the case of non-concordance with two or at least one condition, the non-parametric Kruskal-Wallis test was used to compare the groups. In the case of statistically significant heterogeneity between groups, multiple comparisons were conducted using Dunn’s test. Evaluation of the association between qualitative variables (the three study groups versus groups carrying different genotypes) were performed using the Chi-squared test. All analyses were conducted using STATISTICA 10.0 software (StatSoft, USA). The frequency differences of particular genotypes and alleles between the groups under study were presented as OR and 95% confidence intervals (CI). The concordance of genotype distributions with the Hardy-Weinberg equilibrium was tested using a calculator on the following website: http://ihg.gsf.de/cgi-bin/hw/hwa1.pl [35]. As indicative of statistical significance, we considered P-values below 0.05.