2.5. Statistical Analyses
early-night sleep loss
IBM SPSS Statistics, Version 22 for macOS, was used for all analyses, and values are expressed as mean ± SEM. Since values were not always normally distributed at each time point, data were log transformed for leptin and ghrelin and hunger/appetite data and analyzed using analysis of variance (ANOVA) for repeated measures, including the factors ‘condition’ (for ‘early-night sleep loss’ vs. ‘late-night sleep loss’ vs. ‘regular sleep’) and ‘time’ (for repeated measurements during the experiment). In order to correct for sphericity, Green House Geisser correction was applied if necessary. For pairwise comparisons of non-normalized values at single time points, non-parametric tests were applied, i.e., the Friedman test, as well as the Wilcoxon test. The area under the curves (AUC), using the trapezoidal method, were calculated to examine all-over leptin and ghrelin secretion (from 7:00 h to 11:00 h). A 