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 tobe directly connected. It is unknown to what degree this results from dispositions to formsuch ties (i.e., to close open triangles) per se or from other processes, such as homophily andmore opportunities for exposure. These are difficult to disentangle in many settings, but insocial media not only can they be decomposed, but platforms frequently make decisions thatdepend on these distinct processes. Here, using a field experiment on social media, werandomize the existing network structure that a user faces when followed by a target accountthat we control, and we examine whether they reciprocate this tie formation. Being randomlyassigned to have an existing tie to an account that follows the target user increases tieformation by 35%. Through the use of multiple control conditions in which the relevant tie isabsent (never existent or removed), we attribute this effect specifically to a minimal cue thatindicates the presence of a potential mutual follower. Theory suggests that triadic closureshould be especially likely in open triads of strong ties, and we find larger effects when thesubject has interacted more with the existing follower. These results indicate a substantialrole for tendencies toward triadic closure, but one that is substantially smaller than whatmight be inferred from prior observational studies. Platforms and others may rely on thesetendencies in encouraging tie formation, with broader implications for network structure andinformation diffusion in online networks.