Tendencies toward triadic closure: Field-experimental evidence

Empirical social networks are characterized by a high degree of triadic closure (i.e. transitivity, clustering), whereby network neighbors of the same individual are also likely to be directly connected. It is unknown to what degree this results from dispositions to form such relationships (i.e. to close open triangles) per se or whether it reflects other processes, such as homophily and more opportunities for exposure. These are difficult to disentangle in many settings, but in social media not only can they be decomposed, but platforms frequently make decisions that can depend on these distinct processes. Here, using a field experiment on social media, we randomize the existing network structure that a user faces when followed by a target account that we control, and we examine whether they reciprocate this tie formation. Being randomly assigned to have an existing tie to an account that follows the target user increases tie formation by 35%. Through the use of multiple control conditions in which the relevant tie is absent (never existent or removed), we are able to attribute this effect specifically to a small variation in the stimulus that indicates the presence (or absence) of a potential mutual follower. Theory suggests that triadic closure should be especially likely in open triads of strong ties, and we find evidence of larger effects when the subject has interacted more with the existing follower. These results indicate a substantial role for dispositions toward triadic closure, which platforms and others can choose to leverage in encouraging tie formation, with implications for network structure and the diffusion of information in online networks.