The offline roots of online hostility: Adult and childhood administrative records predict individual-level hostility on Twitter

Reducing hostility in social media interactions is a key public concern. Most extant research emphasizes how online contextual factors breed hostility. Here, we take a different perspective and focus on the offline roots of hostility, i.e., stable individual-level dispositions. Using a unique dataset of Danish Twitter users (N = 4,931), we merge data from administrative government registries with a behavioral measure of online hostility. We demonstrate that individuals with more aggressive dispositions (as proxied by the number of criminal verdicts) are more hostile in social media conversations. We also find evidence that features of childhood environments predict online hostility. Time spent in foster care is a strong predictor, while other indicators of childhood instability (e.g., the number of moves and divorced parents) are not. Furthermore, people from more resourceful childhood environment -- those with better grades in primary school and higher parental socioeconomic status -- are more hostile on average, potentially because such people are more politically engaged. These results offer an important reminder that much online hostility is rooted in offline experiences and stable dispositions. Accordingly, efforts to reduce online hostility may need to broaden the focus to remedy the effects of problematic offline environments.