数字世界:看统计学怎么预测恐怖袭击

What is the risk of a war on the Korean peninsula or South China Sea? Or, for that matter, of another terrorist attack on American soil? These are questions that western diplomats and security experts are asking themselves this spring. And as speculation grows, those officials have been duly scouring satellite feeds, intelligence reports and history books.

朝鲜半岛或南中国海爆发战争的风险有多大？美国本土再次遭遇恐怖袭击的风险又有多大？这是今年春天西方外交人士和安全专家一直在思索的问题。各种猜测四起，这些官员也在理所当然地查找卫星资料，翻阅情报报告和历史书籍。

Over in Colorado, Aaron Clauset, a computational scientist, is pondering the dangers from a different perspective. Clauset, who teaches at the University of Colorado, Boulder and is part of the Santa Fe Institute, has spent the past decade on the frontier of computing and statistical research. But he has not focused on areas normally beloved by geeks, such as engineering, physics or biology.

而在科罗拉多州，计算科学家亚伦·克劳塞特(Aaron Clauset)正从截然不同的角度考量上述风险。克劳塞特在科罗拉多大学博尔德分校(University of Colorado, Boulder)任教，同时还是圣菲研究所(Santa Fe Institute)研究员，他在过去十年内一直奋战在计算和统计研究的前沿。但工程、物理或生物等理科怪才们青睐的领域却不是他的研究重点。

Instead, Clauset and other statisticians, such as Ryan Woodard of the Swiss Federal Institute of Technology in Zurich, have analysed the past 200 years of military conflicts. And this has produced a thought-provoking conclusion: if you look at the global pattern of war and terrorism, human violence has moved in surprisingly stable cycles.

相反，克劳塞特和瑞士联邦理工学院苏黎世分校(Swiss Federal Institute of Technology in Zurich)的瑞恩·伍达德(Ryan Woodard)等统计学家分析了过去200年的军事冲突。他们得出的结论发人深思：对战争和恐怖主义的全球格局研究表明，人类暴力活动的变化规律出奇地稳定。

Indeed, it is so stable that Clauset sees strong parallels between human conflict and earthquakes – at least in statistical terms. He and other researchers are now borrowing models developed from seismology and physics to forecast future patterns of violence. The aim of this “terror physics” (as some dub it) is not to predict exactly where and when a terrorist attack may occur – doing that is as hard as pinpointing the next quake. Instead, these statisticians are working out the likely rate of attacks and wars – to tell when one seems statistically overdue.

确实，规律是如此稳定，以至于克劳塞特发现了人类冲突和地震之间存在密切关系——至少在统计学上是这样的。现在，他在与其他研究人员借鉴由地震学和物理学发展而来的模型，预测未来暴力活动发生的规律。“恐怖物理学”（有些人如此称呼这门学问）的宗旨不是预测恐怖袭击的具体时间地点——这与精确地预测下一场地震一样困难，而是研究出袭击和战争的可能概率，从统计学角度推断出何时可能会发生此类事件。

“The frequency and severity of wars has been pretty constant for 200 years despite all the massive changes in geopolitics, technology and population,” Clauset explains. On average the world sees one new international war every two years and a new civil war about every 1.5 years. And while terrorist attacks typically occur in clusters, with a few “mega” attacks accounting for large numbers of deaths, there are clear statistical rhythms there too. So much so that Clauset and Woodard argue that seemingly “rare” events, such as 9/11, are not actually that extraordinary after all. As they write in a 2012 paper: “Patterns observed in the frequency of severe terrorist events suggests that some aspects of this phenomenon, and possibly of other complex social phenomena, are not nearly as contingent or unpredictable as is often assumed.”

克劳塞特解释道：“尽管200年来地缘政治、科技和人口均发生了剧变，但战争的频率和烈程度一直较为稳定。”世界上平均每两年爆发一次国际战争，约每1.5年爆发一次内战。另外，尽管恐怖袭击通常集中爆发，且少数几次“超级”袭击造成大量死亡，但其中也存在颇为明显的统计规律。于是，克劳塞特和伍达德提出，类似“9·11”恐怖袭击等看似“罕见”的事件其实并不特别。正如他们在2012年的一篇论文中写道：“观察严重恐怖袭击事件得出的规律是，这一现象乃至其他复杂社会现象的某些方面,远不如人们通常以为的那样不确定和难以预料。”

I daresay that some people would consider this analysis to be ridiculous or offensive. After all, we tend to think that the 21st century is a time of great flux, when we are reshaping the world. However, “terror physics” can only predict the future if you think that humans are doomed always to behave in consistent ways, without the capacity for change or progress. That is not a popular idea among governments. Some academics might question it too: the psychologist Steven Pinker, for example, argues that human violence is steadily declining in the world today, at least when measured in terms of violence per capita, as opposed to gross military casualties.

我敢说，有人会觉得这一结论荒诞不经或是招人反感。毕竟，我们倾向于认为21世纪是激变的时代，是我们改造世界的时代。然而，“恐怖物理学”能够预测未来的前提却是，人类的行为方式注定是前后一致的，缺乏改变或进步的能力。这一观点得不到各国政府的认同，也引来一些学者的质疑。例如，物理学家斯蒂文·平克(Steven Pinker)认为，人类暴力活动如今呈现出稳步减少的趋势，至少以人均暴力衡量是如此（但军队总伤亡并非如此）。

In any case, diplomats usually study conflicts in terms of idiosyncratic social and historical factors, not cold data points. Or as Clauset says: “The conflict studies community usually wants to look at the motives of terrorists or their tactics, not the bigger pattern ... it’s like asking a weather forecaster to worry about climate change.”

无论如何，外交人士往往用来分析冲突的依据是特殊的社会和历史因素，而不是冷冰冰的数据点。或如克劳塞特所说：“冲突研究领域通常希望研究恐怖分子的动机或行动手法，而不是总体趋势……这就好比天气预报员为气候变化操心一样。”

But while military experts might be ambivalent about the value of terror physics, Clauset and Woodard’s research is now causing a buzz in the statistical world. It is also attracting serious interest from insurance companies and bankers, who are keen to work out the risks of terrorist attacks. Clauset and his fellow number-crunchers are hoping that the wider policy community starts to pay more attention too.

不过，虽然军事专家对恐怖物理学的价值褒贬不一，但克劳塞特和伍达德的研究已经在统计学界引起轰动。热衷于研究恐怖主义袭击风险的保险公司和银行家也对恐怖物理学产生了浓厚兴趣。克劳塞特和统计学同仁们希望政策群体也能予以更多关注。

If the number-crunchers can persuade governments to recognise that there is a statistical rhythm to violence, their argument goes, countries might be able to mobilise resources in preparation. And if policy makers acknowledge these cycles, they might also start to reflect on a fundamental question: what exactly drives those outbreaks of war or terrorism? Can we always blame violence on idiosyncratic personalities (be that the North Korean leaders, Osama bin Laden or anyone else)? Or is there something about the human condition – or our interaction with the environment – which dooms us to terrorism and war with such regularity?

在他们看来，如果统计学家能说服政府认识到暴力的统计学规律，各国或许能够动用资源进行针对性的防范。如果政策制定者承认暴力发生周期的存在，他们或许还能开始反思一个根本的问题：究竟是什么因素导致战争或恐怖主义活动的爆发？我们能否一成不变地将暴力归咎于怪异的人格（不论是朝鲜领导人、奥萨马·本·拉登(Osama bin Laden)还是别人）？还是说，与人类状况有关的因素——或是我们与环境的互动——让我们不可避免地遭遇规律性的恐怖主义活动和战争？

These are, of course, big philosophical issues. I don’t expect that any government will rush to discuss them publicly soon – not when politicians are busy fighting a “war on terror”, with the unspoken assumption that it is possible for humans to eradicate the scourge. But if nothing else, Clauset’s numbers put the recent past in perspective (by historical standards the Boston attack, for example, looks pretty small). And they should make us think about the future too. Clauset reckons that the chance of seeing another war this century on the same scale as the second world war (with 60m deaths) is 41 per cent. Meanwhile, the chance of a 9/11-size event this decade is between 19 per cent and 46 per cent. This is, of course, still irritatingly vague; but as predictions go, it seems too large to entirely ignore. Least of all in a place such as Boston, London – or even Korea.

当然，这些都是重大的哲学问题。我不指望哪国政府在短期内会公开讨论这些问题——政客们正忙着打“反恐战争”，他们的想法不言自明：人类是可以根除恐怖主义灾难的。但至少，克劳塞特的统计研究全面地检视了近现代历史（比如按历史标准，波士顿遭受的袭击似乎并不严重）。而且，这些研究也应当促使我们思考未来。克劳塞特估计，本世纪爆发一场与二战规模（死亡6000万人）相当的战争的概率是41%，而目前十年里发生严重性堪比“9·11”恐怖袭击的事件的概率介于19%至46%之间。当然有些恼人的是，这些数字仍然过于模糊。但从预测的角度来说，上述概率已大到让我们很难置若罔闻的地步，对于波士顿、伦敦乃至朝鲜半岛这些危险地带就更不容忽视了。