Table 2.

Risk of bias of the included studies

	Authors	Selection bias	Study design	Confounders	Blinding	Data collection	Withdrawals/dropouts
1	Berk-Seligson et al. (2014)	Low risk	Low risk	Low risk	High risk	Low risk	Not applicable
2	Berthelon and Kruger (2011)	Not applicable	High risk	Low risk	Low risk	Low risk	Not applicable
3	Kenney and Godson (2002)	Unclear risk	Low risk	Unclear risk	High risk	Unclear risk	Unclear risk
4	Muñoz-Vallejos and Rosales-Donoso (2008)	Unclear risk	High risk	Unclear risk	High risk	Unclear risk	Not applicable
5	Pérez et al. (2013)	Unclear risk	High risk	Unclear risk	High risk	Low risk	Unclear risk
6	Reyes-Moreno 2011	Unclear risk	High risk	Unclear risk	High risk	Low risk	Unclear risk
7	Silveira et al. (2010)	Not applicable	High risk	Unclear risk	Low risk	Low risk	Not applicable
8	Varela et al. (2009), Tijmes and Varela (2008)	Unclear risk	High risk	Unclear risk	High risk	Unclear risk	Low risk
9	Varela (2011)	Unclear risk	High risk	Unclear risk	High risk	Low risk	Low risk

A systematic review of interventions to prevent youth violence. Latin America, 2015 (using an adaptation of the Quality Assessment Tool for Quantitative Studies)