4. Discussion
HHS
HOLIDAYS
The HHS Study is one of the first studies aimed at preventing stress among young people in high school combining educational and environmental intervention strategies. We found no effect of the HHS intervention on perceived stress in the total study sample nor in specific subgroups. The systematic reviews of school-based interventions for stress prevention concluded that educational strategies show some positive effects in the short term [The mean PSS-10 score increased from the baseline to the follow-up among students at the intervention and control schools. This was expected as the baseline measurement was conducted in the beginning of the school year, immediately after the summer holidays, while the follow-up was conducted close to the beginning of the revision period preceding exams, which is a stressful time for many students. The aim of the intervention was, therefore, to achieve a lower increase in stress levels among students in the intervention group, but the mean PSS-10 score increased equally in both groups.