School-based programmes to reduce bullying and victimisation

School-based anti-bullying programmes were found in a systematic review with meta-analysis (Ng et al., 2020, 17 studies, N= 35 694 adolescents) to have very small to small yet significant effect in:

• reducing traditional bullying and cyberbullying perpetration (traditional:SMD -0.30 and cyber: SMD - 0.16)
• reducing traditional bullying and cyberbullying victimization (traditional: SMD - 0.18 and cyber: SMD - 0.13)

Type of intervention (i.e., whole school–based or classroom-based), program duration, and presence of parental involvement did not moderate program effectiveness, but cyberbullying programs were more effective when delivered by technology-savvy content experts compared to teachers.

The results of a second systematic review with meta-analysis (Fraguas, et al. 2020, 69 RCTs, N = 111 659) support the feasibility of implementing anti-bullying programs in schools and suggest their potential effectiveness. School anti-bullying interventions were found to have small but significant effect in:

• reducing bullying (ES - effect size -, −0.150; 95%CI, −0.191 to −0.109)
• improving mental health problems (ES, −0.205; 95%CI, −0.277 to −0.133) at study end point,
• with PINs -Population Impact Number - for universal interventions that target the total student population of 147 (95%CI, 113-213) and 107 (95%CI, 73-173), respectively. In other words, for an estimated bullying prevalence of 15% (a conservative estimate considering prevalence rates reported in previous studies), an average anti-bullying intervention needs to include 147 (95% CI, 113-213) people to prevent 1 case of bullying and 107 (95% CI, 73-173) people to improve mental health problems. We also found a substantial population impact (PIN, 167; 95%CI, 100-360) for interventions targeting cyberbullying (ie, 167 young people on average need to receive the intervention to prevent 1 case of cyberbullying perpetration or exposure). To put these results into context, the PIN is 35 450 for taking aspirin to avoid 1 death during the 6 months after a first nonhemorrhagic stroke, and the PIN is 324 for human papillomavirus vaccination in girls to prevent cervical cancer.

The duration of intervention was not statistically significantly associated with intervention effectiveness (mean [range] duration of interventions, 29.4 [1 to 144] weeks). The effectiveness of anti-bullying programs did not diminish over time during follow-up (mean [range] follow-up, 30.9 [2-104] weeks).