4.4. Limitations
Measuring the effects of interventions targeting psychosocial aspects is challenging, and the precision of self-report measures is crucial. Although great care was taken to use the appropriate measures, a contributing factor to non-significant effects could be the use of measures that did not capture existing effects. Another aspect to consider is the possibility of ceiling effects. For example, all three school-specific psychosocial constructs (teacher support, classmate support, and caring climate) displayed relatively high mean scores (3.57–4.07 on a scale from one to five) across intervention groups and years. This could indicate that the potential for improvement under school-specific conditions was limited in these schools.Another aspect may be related to the slightly low statistical power of this study and the risk of a Type III error (i.e., rejecting the hypothesis not because there is no effect but because it cannot be detected). The initial power analyses were performed at the class level, as the interventions, especially the DSP, were mainly related to class. However, as the implementation of the DSP by the program owner was intended to be a whole-school measure, randomization was performed with schools as a cluster. Such an intervention usually yields small effect sizes (Cohen’s D = 0.20), while the power in this study could only detect moderate-to-high effect sizes (Cohen’s D = 0.50), thus resulting in the possibility of undetected effects.