Estimating the Effect Size of Moral Contagion in Online Networks: Each message is 12% more likely to be shared for each additional moral-emotional word

Brady, William J., and Jay J. Van Bavel. 2021. “Estimating the Effect Size of Moral Contagion in Online Networks: A Pre-registered Replication and Meta-analysis.” OSF Preprints. April 7. doi:10.31219/osf.io/s4w2x

Abstract: Over 4 billion people now use social media platforms. As our social lives become more entangled than ever before with online social networks, it is important to understand the dynamics of online information diffusion. This is particularly true for the political domain, as political elites, disinformation profiteers and social activists all utilize social media to gain influence by spreading information. Recent work found that emotional expressions related to the domain of morality (moral emotion expression) are associated with increased diffusion of political messages--a phenomenon we called ‘moral contagion’. Here, we perform a large, pre-registered direct replication (N = 849,266) of Brady et al. (2017), as well as a meta-analysis of all available data testing moral contagion (5 independent labs, 27 studies, N = 4,821,006). The estimate of moral contagion in the available population of studies is positive and significant (IRR = 1.12, 95% CI = [1.06, 1.19]), such that each message is 12% more likely to be shared for each additional moral-emotional word. The mean effect size of the large, pre-registered replication (IRR = 1.15) better estimated the effect size of the available population of studies than the original study (IRR = 1.20). These findings reinforce the importance of replication and producing a pre-registered analysis to generate accurate estimates of effect size for future studies.