Dr. Andrea Baronchelli from City University of London, "How norms change: New evidence from data and experiments"

Researchers and policy makers agree that new social norms could help solve large-scale problems, from climate change to antibiotic resistance. However, our understanding of how norms change has been limited so far by the lack of suitable data. In this talk, I will discuss two recent studies that shed light on this process. In the first [PNAS 115, 8260 (2018)], we examined linguistic norm shifts in English and Spanish. We identified three main drivers of norm change that leave markedly different signatures in the data, namely (i) authority, (ii) informal institutions and (iii) a bottom-up process triggered by a small number of committed users (akin to a 'critical mass' phenomenon). We proposed a simple model that reproduces the empirical observations. In the second study [Science 360, 1116 (2018)], we focused on critical mass theory and tested it experimentally in artificial social networks. We let a group of individuals evolve their own social convention. Then, once the agreement was reached, we introduced few confederates pushing for a different norm. As their number crossed a tipping point - roughly 25% of the group size – the whole population would follow them and adopt the new norm. This is the first empirical evidence for the widely adopted theory of critical mass. These results will help better understand both how norms change spontaneously in our societies and how to design effective policies to foster collective behavioural change.