Big Brother 101

Uncovering the True Mastermind

Who´s the most important player in a group? Who´s merely peripheral? Data crunchers find out by plotting people as â€nodes†on computerized graphs, forming web-like networks. The links between nodes are then weighed and analyzed using matrix algebra and other tools.

How close are you and your cellphone records to a terrorist? If the whole country is your potential database, finding the answer might seem like Six Hundred Degrees of Separation. Investigators measure these three qualities when assessing any links:

1. Connectedness
   
   In the simplified network [below] developed by Carnegie Mellon´s David Krackhardt, Diane is the hub with the highest â€degree centrality,†gauged by dividing the number of nodes (people) reached by the total nodes in the network. Diane looks like the key. But take her out, and communication still flows.
2. Betweenness
   
   The real heavy hitters are often the brokers who bring together different constituencies. They have the highest degree of â€betweenness,†measured by the number of times communications must pass through someone on the network. Heather, for instance: If you were to remove her from the network, the right side couldn´t communicate with the left. If this were an Al Qaeda cell, she´d be the one to lock up.

3. Closeness
   
   The number of times people are on a geodesic-the shortest possible path between two others-is also vital. These direct connections allow them to reach a maximum number of nodes in a minimum number of steps. In this group, Fernando and Garth can monitor (and control) information passing through the network. Everyone else is basically playing the game â€telephone,†with one person giving another a message, and so on, degrading communications at each step. Fernando and Garth more or less skip the game and talk to people directly, so they´re better informed. If you´re looking to eavesdrop, â€close†people, like Fernando and Garth, would be your best bets.

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