*2.5. Statistics*

Quantitative variables were summarized as mean values and standard deviation, or by median and interquartile range, depending on the symmetry of the data distribution. Variables with normal distribution were expressed as mean values and standard deviation, whereas those variables with non-normal distribution were shown as median and interquartile ranges. Normality of quantitative variables was analyzed by the Shapiro Wilk test. Variables with normal distribution were compared using Student's t test for independent and paired samples, while variables with non-normal distribution were compared using the Mann–Whitney U test for independent samples, and a Wilcoxon Signed Rank test for relate samples. Associations between variables were studied by the univariate linear regression or quantile regression. Values of *p* < 0.05 were considered significant. Statistical analyses were performed using the statistical package for social science (SPSS, IBM, Armonk, NY, USA), version 26.0.
