How can we interpret the recent spate of terrorist attacks in the USA, France and Britain? In 2012 the START Global Terrorism Database (GTD) recorded a total of nearly 7,000 terrorist attacks worldwide, resulting in more than 11,000 deaths and 21,000 injuries.

Terrorism has two characteristics that make it especially prone to myth-making – its “black swan” nature and the fact that it is “bursty. Essayist Nassim Taleb defines a black swan incident as one that falls outside the realm of regular expectations, has a high impact and defies predictions. Taleb claims that the coordinated terrorist attacks of 11 September 2001 in the United States are a perfect example of a black swan event because they were unexpected, had a huge impact on policy and were difficult to predict. One of the major challenges in responding to terrorism is that a handful of very rare cases can have a disproportionate effect on setting the agenda for the phenomenon more generally.

But terrorism also tends to be bursty. Bursty distributions are those that are highly concentrated in time and space. Recent research has shown that diverse phenomena are bursty, including streams of e-mail messages; traffic on crowded freeways; the frequency of forest fires; and the global distribution of terrorism. These two qualities – its black swan and bursty character – make responding to terrorism challenging. On the one hand, terrorism is relatively infrequent and hard to predict; on the other hand, when it starts to happen there is a tendency for it to occur in the same place a lot.

The GTD can help us put these characteristics of terrorism into context. It now includes over 110,000 terrorist attacks from everywhere in the world that took place from 1970 until 2012.

The database debunks five myths about terrorism that have been strongly influenced by black swan events like 9/11. I call these myths in the everyday sense in that they are conclusions that are fictitious or unscientific.

First, the tremendous impact of 9/11 encourages us to think about terrorism as being mostly about dissatisfied individuals from one country attacking innocent civilians from another country. Based on the data in the GTD we found that more than 90% of the 17,000 attacks carried out by 52 foreign terrorist groups were actually domestic attacks.

Second, because of the seemingly irrational nature of the 9/11 al-Qa’ida attack, it is easy to lose sight of the fact that a large number of terrorist attacks involve fairly rational political disputes over territory. Although there are major differences in terms of their specific orientation, this explains in large part all of the top ten most active terrorist groups of the modern era, including Shining Path, ETA, the FMLN, the IRA, FARC, Hamas and the LTTE.

Third, because of the devastation caused by attacks such as 9/11, it is easy to suppose that most terrorist attacks are incredibly lethal. However, from the GTD we find that more than half of all terrorist attacks since 1970 involved no fatalities.

Fourth, images of 9/11 and Hollywood movies no doubt encourage us to think that most terrorist strikes depend on sophisticated weaponry. But contrary to this view of terrorism that we commonly get from Hollywood, the vast majority of terrorist attacks rely on unsophisticated, readily accessible weapons. According to the GTD, 80% of all attacks rely on explosives and widely available firearms.

And finally, the advance planning, originality and destructiveness of 9/11 contributed to the notion that terrorist groups are infallible. We could call this the myth of the “super-terrorist”. My colleagues and I at the START Center have been involved in several research projects using GTD data which suggests otherwise. For example, in a recent study we used the GTD to examine the targeting strategies of the Armenian Secret Army for the Liberation of Armenia (ASALA) – a very active group based in Turkey. The increasing reliance on random, brutal violence such as the attack by ASALA on Orly Airport created a polarized and hostile climate among the supporters of ASALA and seriously undermined its legitimacy.

So, if rare events like 9/11 are black swan events, why not simply ignore them and go back to business as usual? A major reason why ignoring terrorism is a risky idea is directly related to the fact that it is bursty: when it starts to happen it happens a lot and rapidly.

If we look at worldwide terrorism over the past four decades, we find not one single kind of terrorist threat, but rather successive waves of attacks by groups with very different ideologies and goals. The common pattern is that a group or set of groups gets organized, stages increasing numbers of attacks and then decline. In fact, this bursty nature of terrorism might eventually help us become more effective in responding to terrorist threats.

While these results are preliminary, they give us reason to hope that analysis of the spatial and temporal patterns of terrorism might eventually help to guide our policies on countering terrorism.

And this is the challenge that terrorism raises for contemporary societies: there are dangers in overreacting but there are also dangers in not reacting. Fortunately, terrorist attacks like 9/11 have turned out to be rare – like black swans. Unfortunately, the threat of sudden bursts of terrorist attacks is likely to be a permanent feature of the twenty-first century.

Author: Gary LaFree is Director of the National Consortium for the Study of Terrorism and Responses to Terrorism (START), and a member of the World Economic Forum’s Global Agenda Council on Terrorism

Image: A bomb unit robot investigates a suspicious vehicle in New York City REUTERS/Lucas Jackson