Statistical Analysis and Ethical statement
To test the differences among groups, chi-square test was used for categorical data, while Student’s t test was used for continuous data. Probability values lower than 0.05 were considered statistically significant. All analyses were performed with the STATA 12.1 software (Stata Corp., College Station, TX, USA).
Given the retrospective nature of the study and anonymity, Ethic Committee approval was not required.