Statistical analysis
We have expressed quantitative variables as
mean ± standard deviation, and qualitative variables
as frequency distributions. We assessed the normality of the
data by means of the Kolmogorov---Smirnov test. Quantitative variables were compared by means of Student’s t test
or the Mann---Whitney U test, depending on whether their
distribution was normal or not, respectively. We analysed
the data with the statistical software IBM-SPSS version 21.0
for Windows. The level of statistical significance was set at
0.05.