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