  Several centrality measures have been formulated to quantify the notion of
'importance' of actors in social networks. Current measures scrutinize either
local or global connectivity of the nodes and have been found to be inadequate
for social networks. Ignoring hierarchy and community structure, which are
inherent in all human social networks, is the primary cause of this inadequacy.
Positional hierarchy and embeddedness of an actor in the community are
intuitively crucial determinants of his importance. The theory of social
capital asserts that an actor's importance is derived from his position in
network hierarchy as well as from the potential to mobilize resources through
intra-community (bonding) and inter-community (bridging) ties. Inspired by this
idea, we propose a novel centrality measure SC (Social Centrality) for actors
in social networks. Our measure accounts for - i) an individual's propensity to
socialize, and ii) his connections within and outside the community. These two
factors are suitably aggregated to produce social centrality score. Comparative
analysis of SC measure with classical and recent centrality measures using
large public networks shows that it consistently produces a more realistic
ranking of nodes. The inference is based on the available ground truth for each
tested networks. Extensive analysis of rankings delivered by SC measure and
mapping with known facts in well-studied networks justifies its effectiveness
in diverse social networks. Scalability evaluation of SC measure justifies its
efficacy for real-world large networks.
