Figure 2.

Different methodological approaches to study aggression in the data set. Number of articles (a) using the different methodological approaches to assess aggression, and proportion of articles (b) using the different methodological approaches before 2000, between 2001 and 2010 and after 2011. The color scheme for the different methodological approaches used in (a) also applies to (b). The proportion of increased, decreased and no effect on aggression varied between the use of home cage observation, test for aggression and wounding for assessment (c). In panel (c), observations using more than one methodological approach have been excluded.