Author
Valdis E. Krebs
1 reading card from 1 book · 2002.
1 card
Mapping Networks of Terrorist Cells · 2002
Degree, betweenness, closeness — three rankings, not one; and a missing tie is usually missing collection.
Krebs reconstructed from public sources the network of the 19 hijackers of 11 September and measured it. Mohamed Atta had the highest degree (0.417) and the highest closeness (0.571), but not the highest betweenness: there Nawaf Alhazmi led (0.334 against 0.318). His conclusion is cautious and instructive: the metrics "do not necessarily confirm" leader status, because "we are obviously missing nodes and ties". A covert network is built to look different from what it is — sparse ties, cells that touch through a single person, members who do not know each other. Low density is a security choice, not an organisational weakness. The three measures answer different questions. Degree: who is the most active in contacts — good for finding hubs, bad for finding who controls the flow. Betweenness: who sits on the most shortest paths between others — the person whose removal breaks the network into pieces; often a discreet one. Closeness: who reaches everyone in the fewest steps — who learns first. An analysis that reports a single ranking hides the structure. The traps, in order of frequency: confusing co-appearance in the same documents with a relationship (two names in one article are not a tie); forgetting that a missing tie in the data is usually missing collection, not a missing relationship; treating centrality as guilt. Krebs writes explicitly that his map is incomplete and that mapping is a stage, not a conclusion. For olivLaw the rule is the same as in the lesson on actors: an affiliation is asserted only with a source, and co-occurrence is called co-occurrence.
“Analyzing networks after an event is fairly easy for prosecution purposes. Mapping covert networks to prevent criminal activity is much more difficult.”