*2.2. Measures*

Online Hate Involvement. To measure online hate involvement, three items were adopted from the work of Hawdon et al. [2]. For assessing those who were bystanders of online hate, participants were asked: "How often in the past 12 months have you observed hateful or degrading writing or speech online, which inappropriately attacks certain groups of people or individuals because of their sex, religious affiliation, race, or sexual orientation?". For online hate perpetration, they were asked: "How often in the past 12 months have you posted hateful or degrading writing or speech online, which inappropriately attacks certain groups of people or individuals based on their sex, religious affiliation, race, or sexual orientation?". For online hate victimization, they were also asked: "How often in the past 12 months have you personally been the target of hateful or degrading writing or speech online because of your sex, religious affiliation, race, or sexual orientation?". Participants rated each item on a scale of 0 (never) to 4 (very frequently).

Toxic Online Disinhibition. The four-item Toxic Online Disinhibition Scale assessed the extent to which adolescents believed that they were less inhibited while interacting or engaging in certain behaviors online, with response options ranging from 0 (definitely do not believe) to 4 (definitely do believe) [22]. A confirmatory factor analysis revealed a good fit of the toxic online disinhibition scale: *χ*2 = 29.33, *df* = 8, *p* < 0.001, comparative fit index (*CFI*) = 0.99, Tucker–Lewis index (*TLI*) = 0.99, root mean square error of approximation (*RMSEA*) = 0.04, and standardized root mean square residual (*SRMR*) = 0.01. A mean score was computed by averaging all items. Cronbach's alpha was 0.79.

Control Variables. Participants were asked for their age and sex to determine demographic characteristics. Migration background was assessed by asking which language is mainly spoken at home. Family socioeconomic status was measured with the Family Affluence Scale (FAS) [24]. The FAS was trichotomized into low, medium, and high socioeconomic status.
