Mechanisms of change: what explains shifts in online immigration discourse after terror attacks?

In this paper, we discuss and test the mechanisms that produce changes in online debates following unexpected events. In particular, we analyze how the Swedish online discourse on immigration changes in the wake of Jihadist terrorist attacks in Europe. We test the role of two mechanisms that may drive shifts in online discussions: changes in (1) how individuals talk about immigration (within-individual change) and (2) the composition of individuals who participate in debates (compositional change). In order to evaluate the contribution of these two mechanisms, we analyze a corpus of 664k immigration-related texts posted on Sweden’s largest discussion forum, Flashback, between 2010 and 2020 and study the impact of 37 terrorist attacks in Sweden and other Western European countries. Using a seeded topic modeling approach, we compare the relative salience of different themes in discussions about immigration before and after the attacks. Whereas aggregate-level analyses of social media data often interpret shifts as being due to individual-level changes, we show that the change in the composition of discussants also contributes to shifts. Our findings highlight the necessity of individual-level text data as a means of differentiating two separate mechanisms that can produce similar shifts in aggregate measures of discourse.