Arseneault et al.'s paper (2010) examines whether bullying victimization is an essential risk factor for mental health problems, and hence should be targeted by treatment and prevention programmes. This is a highly relevant topic, and the authors provide an excellent overview of up-to-date research. Their conclusion that (a) bullying victimization is associated with severe mental health consequences, and (b) efforts should be focused on reducing bullying victimization, is highly convincing.

An important issue in bullying research is the assessment of bullying victimization. The authors critically discuss methods based on self-reports versus peer nominations. We feel that it is important to take this discussion forward by focusing more on the complementary nature of each method, rather than on the supposed superiority of either method. Thus, both approaches are valid, and both are also susceptible to certain biases (Pellegrini, Reference Pellegrini, Juvonen and Graham2001; Olweus, Reference Olweus, Jimerson, Swearer and Espelage2010). Self-reports provide a unique, individual source of information, tapping behaviours that could easily go unnoticed by others. At the same time, this subjective view is susceptible to social desirability, and consequently might result in over- or under-reporting. Peer nominations, on the other hand, are less susceptible to this subjectivity, as multiple observers are used. However, peer nominations are flawed in that relevant behaviours or gestures can be missed in some cases, and nominations may be based on wrong or insufficient information.

Because self-reports and peer nominations measure different constructs (i.e. individual versus group perceptions), they present complementary information. Comparing the data collected with both methods will lead to either converging or diverging results. Whatever the outcomes, we can then potentially employ three research strategies for identifying bullies and victims. In the case of converging results, we get victims (or bullies) identified as such by both methods (minimum strategy, leading to some false negatives). However, we can also employ a maximum strategy by accepting victims (or bullies) as such because they were identified by at least one method (leading to some false positives). Finally, we could use a differential strategy, distinguishing between exclusively self-reported victims (bullies), exclusively peer-reported victims (bullies) and converging victims (bullies). Alternatively, one could use peer reports to identify bullies, but self-reports to identify victims. However, it would still be necessary to employ both measurement methods.

Peer-reported victimization has been associated with more rejection and less acceptance in the group, whereas self-reported victimization has been associated with self-reported adjustment outcomes (i.e. depressed mood, anxiety, loneliness and negative self-views) (Juvonen et al. Reference Juvonen, Nishina, Graham, Juvonen and Graham2001). Overall, self-report methods are more strongly linked to internalising problems, whereas peer nominations are better at predicting the status of the victims and the bullies in interpersonal relationships. Using both methods (peer- and self-reports) with the possibility of employing different strategies will advance our knowledge of bullying and victimization more than simply employing either one or the other method.