Fig. 6

Perceived norm of alcohol consumption in median glasses per week during course periods among Flemish university students before (2021) and after (2023) a social norms approach intervention on alcohol use, separately for females (a) and males (b) . The results of the bootstrapped linear regression models on the secondary outcome for females and males separately are presented in Additional file 3. For females, the bootstrapped model on the perception of alcohol consumption (Table A3.1) was significant, with R² = 0.010, F (7,6825) = 10.054, p < .001. According to the outcome of the model, female students from the intervention group at endline estimated the alcohol consumption of their peers significantly lower than the control group (bootstrapped p = 0.045; B = -1.643, bootstrapped CI = -3.297 to -0.222). However, the outcome of the significant bootstrapped linear regression model for males (R² = 0.004, F (4,4110) = 3.836, p = 0.004, see Table A3.2), did not show a significant effect of the intervention over time (bootstrapped p = 0.158; B = -2.354, bootstrapped CI = -5.785 to 0.363)