Abstract: All over the world intelligence services are collecting data concerning possible terrorist threats. This information is usually transformed into network structures in which the nodes represent the individuals in the data set and the links possible connections between these individuals. Unfortunately, it is nearly impossible to keep track of all individuals in the resulting complex network. Therefore, Lindelauf et al. (2013) introduced a methodology based on a game theoretic centrality measure, which is innovative in the sense that it takes into account not only the structure of the network but also individual and coalitional characteristics of the members of the network.
Husslage et al. (2015) perform a sensitivity analysis on the rankings derived from this centrality measure for the case of Al Qaeda s 9/11 attack. In this sensitivity analysis we consider firstly the possible additional information available about members of the network, secondly, variations in relational strength and, finally, the absence or presence of a small percentage of links in the network. We also introduce a case specific method to compare the different rankings that result from the sensitivity analysis and show that the new centrality measure is robust to small changes in the data. The calculation of the Shapley value plays an important role in this methodology. Since the Al Qaeda 9/11 network can be represented by relatively small networks, the determination of Shapley value is not time consuming. However, in larger networks the Shapley value may not be determined in polynomial time. A small improvement to approximate the Shapley value is discussed.