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And after a lengthy delay, the Department of Homeland Security turned down a grant proposal to develop prediction tools based on his research — in part, Clauset says, because "the reviewer thought the tools would be too complicated for the typical DHS worker to understand."
The complex nature of Clauset's work could indeed be part of the problem, says LaFree: "He's working in a pretty rarefied atmosphere in terms of mathematics and statistics. A lot of policymakers don't speak that language." Then again, Clauset's findings don't mix well with the shortsighted nature of most policy work. "This isn't going to be useful to help say what Homeland Security should do next month or next year," LaFree explains. "It is more of a long-term tool."
And Clauset and his colleagues continue to drill into terrorism data. For example, they've determined that explosive devices account for nearly half of terrorism-related deaths. While the finding isn't earth-shattering, it drives home the importance of trying to limit would-be terrorists' access to bomb-making materials. More surprising was their discovery that while larger, more experienced terrorist groups generate a lot more attacks than smaller, unsophisticated groups, when you compare individual attacks, the smaller groups are just as effective at generating casualties. In other words, while focusing resources on defeating major terrorist networks might curtail the overall number of terrorist strikes, it won't necessarily stop major attacks from occurring, since tiny terrorist cells are just as likely to pull off a major catastrophe.
In 2010, Clauset, Young and Gleditsch, along with Lindsay Heger, a political scientist now working at the Broomfield-based One Earth Future Foundation, narrowed in on a specific violent struggle: the ongoing Israeli-Palestinian conflict. And what they've found by analyzing the 3,017 terrorist events associated with this conflict since 1968 could prove relevant to both sides in the struggle. They determined that a tit-for-tat strategy of violent countermeasures sometimes used by the Israeli military was ineffective in quelling violence, and discovered that suicide attacks orchestrated by Palestinian groups were similarly impractical, since they did little to improve the operations' approval ratings among their constituents.
And Clauset continues to consider the underlying promise of terrorism's power-law pattern: its ability to help predict the frequency and severity of future attacks. A 2005 preliminary draft of his original power-law paper caught media attention because it predicted another 9/11-scale attack within seven years — but Clauset and his co-authors removed the prediction from the final version because they believed it wasn't accurate enough. At the prestigious Joint Statistical Meetings this August, however, Clauset and Woodard will return to the prediction issue: They will present new research concluding that if the level of terrorism violence remains stable — as it has, more or less, for decades — there's roughly a 30 percent chance of an attack similar to 9/11 in the next decade. To hedge their bets, they'll also note that if terrorism violence begins to ebb, that chance drops to just 7 or 8 percent. But if terrorism gets worse, the chances of another 9/11 increase significantly — to 80 percent.
Clauset and his colleagues have avoided predicting the likelihood of a larger event — the sort of chemical, biological or nuclear attack that could kill hundreds of thousands of people. "We weren't confident there is enough data to build a model that could make a scientifically based prediction there," explains Clauset.
Still, just as his research drives home the fact that 9/11 should have been conceivable before it occurred, it also suggests that magnitude-9 terrorism is far from impossible. "If we believe the power law is a fundamental property of terrorism — and it appears to be so in a very robust way — it's reasonable to conclude that there may be 'really big terrorism,' this other category involving chemical, biological or radiological attacks. And almost surely, the probability of these kinds of events is much higher than people might expect," he concludes. "If we don't have some people thinking about this in the long term, we are going to be very surprised. We are going to be unprepared."
It's early morning, and the Clauset household is busy. Aaron Clauset sips warily at a cup of coffee he's holding in one hand; he's recovering from a respiratory infection, not to mention jet lag. He's just back from a conference in Zurich, and later this week, he and his family are off to Copenhagen for another series of academic talks. Parker, his ten-month-old daughter, fidgets in his other arm. She doesn't feel like eating this morning, just like she often doesn't feel like sleeping, preferring to keep her parents up much of the night. It doesn't help that their baby-food maker is currently on the fritz; in the kitchen, Lisa is trying to purée steamed pears into edible mush.
Nevertheless, Aaron remains calm, playing happily with Parker. That's the way he usually is at home. "In the academic world he might come off as all business," Lisa says, "but for me, he's really sweet and loving and understanding and warm."
The serene scene stands in stark contrast to the dreadful scenarios that Clauset explores at CU. With the hard-and-fast statistical rules he's uncovering about the way the world works, it's as if he's chipping away at the concept of free will, the concept of being able to change the future, one data point at a time. Despite billions spent on security efforts, Clauset has found that the frequency of major terrorist attacks over the past 35 years hasn't changed...at all.