Following the original interpretation of the Shapley value (Shapley, 1953a)
as a priori evaluation of the prospects of a player in a multi-person iteraction situation,
we propose a group value, which we call the Shapley group value, as a priori evaluation
of the prospects of a group of players in a coalitional game when acting as a unit. We
study its properties and we give an axiomatic characterization. We motivate our
proposal by means of some relevant applications of the Shapley group value, when it is
used as an objective function by a decision maker who is trying to identify an optimal
group of agents in a framework in which agents interact and the attained benefit can be
modeled by means of a transferable utility game. As an illustrative example we analyze
the problem of identifying the set of key agents in a terrorist network.This research has been supported by I+D+i research project MTM2011-27892 from the Government of Spai
