Statistical analysis For the statistical analysis, Stata 11.0 (StataCorp, College Station, TX, USA) will be used. The descriptive analysis will be composed of medians and proportions according to the nature of the variables, with their respective 95% confidence intervals. As a dispersion measurement the Standard Deviation will be calculated. The distribution of the variables will be studied using the Shapiro-Wilk test and the homoscedasticity of the variances with the Levene test. To detect any difference between the groups, a T-test or a Mann Whitney test will be performed according to the distribution of the variables. The categorical variables will be compared using the Chi Squared test or the exact Fisher's test. If required, a multiple logistic regression or a covariance analysis will be performed.