More experts are stepping up to tell us what Valdis Krebs said here last week: be careful with those call-chains, NSA.
"Not every link is as useful as the next," notes Jeff Jonas, who data-mined for both Washington and Las Vegas heavyweights. "Not only must one start with a bad guy but also pursue relationships in a very narrow manner."
Employees who handle cash who are roommates with gaming felons present some risk. Employees would be expected to disclose such. Is this a telltale sign of a criminal intent or a crime? Not in the least! Is this something worth a little more attention than my mom? Well when it comes to casinos, and their expected levels of due diligence, the answer is yes.
What kind of data proves useful in expressing a close personal relationship? Well this generally involves either shared resources (homes, cars, phones) or personal communications (e.g., calls, emails, care packages, money wires). There are a few others, but I will have to let your mind wander as I would hate to tip off any evil doers.
Even when starting with a bad guy, and following only close, personal relationships, the usefulness of the trail still degrades very quickly. That is unless the trail leads to another previously known bad guy then of course, those in between are certainly a bit more interesting.
Meanwhile, over at the Times, Jonathan David Farley notes "a second problem with the spy agency's apparent methodology." It's "in the way terrorist groups operate and what scientists call the 'strength of weak ties.'"
As the military scientist Robert Spulak has described it to me, you might not see your college roommate for 10 years, but if he were to call you up and ask to stay in your apartment, you'd let him. This is the principle under which sleeper cells operate: there is no communication for years. Thus for the most dangerous threats, the links between nodes that the agency is looking for simply might not exist.
If our intelligence agencies are determined to use mathematics in rooting out terrorists, they may consider a profiling technique called formal concept analysis, a branch of lattice theory. The idea, in a nutshell, is that people who share many of the same characteristics are grouped together as one node, and links between nodes in this picture called a "concept lattice" indicate that all the members of a certain subgroup, with certain attributes, must also have other attributes.
For formal concept analysis to be helpful, you need much more than phone records. For instance, you might group together people based on what cafes, bookstores and mosques they visit, and then find out that all the people who go to a certain cafe also attend the same mosque (but maybe not vice versa).
