Gaussian distribution of the data wil be tested by the Kolmogorov-Smirnov test. Data will be presented as mean ± standard deviation (SD). Comparisons between groups will be made with Wilcoxon matched-pairs test or ANOVA when appropriate. Relationships between data will be assessed by Pearson correlation, a Principal Components Analysis or a multivariable generalized estimating equations model when appropriate. Significance will be accepted at the p<0.05 level. Statistical procedures will be performed using SPSS Advanced Statistics software (SPSS Inc., Chicago, IL).