To evaluate the changes in time of the mean results of particular questionnaires the variance analysis (ANOVA) with repeated measurements was used. This analysis requires the fulfilment of the assumption about the compatibility of empirical distributions of the studied questionnaires with the theoretical normal distribution, as well as meeting the assumption of sphericity. The compliance of the distributions was tested using the Shapiro-Wilk’s test, while the verification of the zero hypothesis about the occurrence of sphericity was based on the Mauchley’s test. In case of non-compliance of the assumption about the normality, the non-parametric equivalent of the variance analysis with repeated measurements – Friedman’s test– was used to the analysis of comparisons of mean results over time.