Bayesian Social Influence in the Online Realm

  • Przemyslaw Grabowicz (The Max Planck Institute for Software Systems, Saarbrucken, Germany)
E1 05 (Leibniz-Saal)


Our opinions, which things we like or dislike, depend on the opinions of those around us. Nowadays, we are influenced by the opinions of online strangers, expressed in comments and ratings on online platforms. Here, we perform novel "academic A/B testing" experiments with over 2,500 participants to measure the extent of that influence. In our experiments, the participants watch and evaluate videos on mirror proxies of YouTube and Vimeo. We control the comments and ratings that are shown underneath each of these videos. Our study shows that from 5% up to 40% of subjects adopt the majority opinion of strangers expressed in the comments. Using Bayes' theorem, we derive a flexible and interpretable family of models of social influence, in which each individual forms opinions stochastically following a logit model. The variants of our mixture model that maximize Akaike information criterion represent two sub-populations, i.e., non-influenceable and influenceable individuals. The prior opinions of the non-influenceable individuals are strongly correlated with the external opinions and have low standard error, whereas the prior opinions of influenceable individuals have high standard error and become correlated with the external opinions due to social influence. Our findings suggest that opinions are random variables with varying standard deviations, which are updated via Bayes' rule. Based on these findings, we discuss how to hinder opinion manipulation in the online realm. At the end of my talk, I introduce our project entitled "Current Affairs 2.0: Agenda Setting in the European Union" (

Antje Vandenberg

Max Planck Institute for Mathematics in the Sciences (Leipzig), Germany Contact via Mail

Eckehard Olbrich

Max Planck Institute for Mathematics in the Sciences (Leipzig), Germany

Sven Banisch

Max Planck Institute for Mathematics in the Sciences (Leipzig), Germany