Figure 3.

Comparison of sleepiness during classes according to bedtime on weekdays in each survey. For each bedtime on weekdays, the comparison of degree of sleepiness during classes between each survey was performed using χ² analysis. For each bedtime on weekdays, a comparison of internet use duration (in minutes) on weekdays among groups as per survey year was made using ANOVA. A post hoc analysis between the group from survey III and the groups from the other surveys (survey I and II) was performed using Dunnett’s test.