**2.4 Statistical analysis**

The figures resulting from the data collection are shown as percentages (%) and means (M) including the respective standard deviations (SD) or confidence intervals (95% CI). The subsequent statistical analysis (descriptive statistics, Student's t-test, analysis of variance, χ2 test, Pearson's correlation, and multiple logistic regression analysis) was performed using the software package *Statistical Packages for the Social Sciences* version 20.0 (Chicago, IL, USA). A probability value (p-value) <0.05 was established as the level of statistical significance.

Adequate information of the proceedings and potential implications was delivered to the parents and/or legal guardians, and the corresponding consent was required prior to the inclusion in this study in all cases. The study was presented and approved after the evaluation of the Ethics Committee for Human Investigation at our institution (in line with the ethical standards stated in the Declaration of Helsinki, 1964, and later amendments).
