Shared neighbours provide a topological signal for predicting future or missing network edges.

In a network snapshot, two unconnected nodes may occupy overlapping local neighbourhoods. Common neighbours then act as structural evidence of proximity: co-authors who share collaborators, for example, may be more likely to collaborate later. Liben-Nowell and Kleinberg formalised this link-prediction problem and found that several proximity measures performed 40 to 50 times better than chance on their data, though exogenous events remain difficult to infer from topology alone.