Influence in Terrorist Networks: From Undirected to Directed Graphs

The methodology converts undirected graphs (graphs having links without direction) to directed graphs that indicate influence in one-way or two-way directions, which offers researchers an understanding of the flow of influence in terrorist or other networks. In order to avoid the complication of introducing additional information into an undirected graph in order to make it directed in terms of influence, the methodology calls for the directed graph to be simplified by grouping individuals into “mutual influence sets” which describe the influence each individual directly or indirectly exerts on other individuals in the set. The final step of the methodology calls for the mutual influence sets to be arranged hierarchically from the top to the bottom level so that influence always flows downward. In this type of application, influence is measured by visits, communication traffic, and other contacts. The authors apply this methodology to 2 terrorist networks: 1 involving the 19 hijackers of the September 11, 2001, attacks and 1 involving a much larger and complex network of 62 individuals. Through the construction of the simplified directed graph it becomes apparent that the larger terrorist network actually has a well-defined hierarchical structure, which is consistent with what is known about its leaders and the types of operations it subsumes. The authors warn that when applying this methodology, terrorist networks should be analyzed with a critical eye because they may be manipulating outside observers by doing such things as increasing “chatter” to create the false impression of activity. The authors also note that the methodology can be applied to more benign networks. Figures, notes, references