1. A method comprising, by one or more computing devices: maintaining one or more data stores storing a social graph comprising a plurality of nodes and a plurality of edges between the nodes, the nodes comprising user nodes corresponding to users of a social-networking system and concept nodes corresponding to concepts, each of the edges being associated with a similarity number that indicates an affinity between the nodes that the edge is between; determining a confidence score between a first one of the user nodes and a first one of the concept nodes based at least in part on one or more similarity numbers associated with one or more edges between the first one of the user nodes and the first one of the concept nodes in one or more hops between them on the social graph; and storing the confidence score in the data stores.